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Research Article
Morphological diversity of pistil stigmas and its taxonomic significance of representatives of holoparasitic Orobanchaceae from Central Europe
expand article infoKarolina Ruraż‡, Renata Piwowarczyk‡
‡ Jan Kochanowski University, Kielce, Poland

Corresponding author: Karolina Ruraż ( karolina.ruraz@ujk.edu.pl )

Academic editor: Eberhard Fischer
© 2022 Karolina Ruraż, Renata Piwowarczyk.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Ruraż K, Piwowarczyk R (2022) Morphological diversity of pistil stigmas and its taxonomic significance of representatives of holoparasitic Orobanchaceae from Central Europe. PhytoKeys 215: 1-25. https://doi.org/10.3897/phytokeys.215.96263
Open Access

Abstract

The stigma is the terminal part of the carpel which receives pollen during the pollination process. Although the role of the stigmas in pollination is the same for all angiosperms, stigmas structures are very diverse. This study aimed to evaluate intraspecific, interspecific and intergeneric stigmas variability and then find differences of the stigma morphology amongst 24 holoparasitic Orobanche and Phelipanche species and provide new insights into its potential taxonomic value. This paper was also focused on selecting the best diagnostic features that would be used for future stigma analysis in other species of Orobanchaceae. These analyses were conducted with fresh, dry and fixed material using stereomicroscopy from different locations from Central Europe. Twenty-one quantitative or qualitative morphological features were analysed. This study highlights the variation of stigma morphology and characters which are useful to improve the taxonomic understanding of problematic taxa. Thus, two main types of stigmas were established, based on tested features: 1–oval, rarely hemispherical in shape, most often one-coloured with lobes separated in Phelipanche stigmas; 2–spherical to hemispherical, rarely oval, multi-coloured with partially fused or separated lobes in Orobanche stigmas. The best diagnostic features of the stigmas for distinguishing the Orobanchaceae are the type and subtype of stigma, the length and area of the stigma, the width of single lobes, the width in the middle part of the stigma, the length of upper and lower separation in the middle part between lobes and the angle between lobes in the upper and lower part. The morphological features of the stigmas are important criteria for distinguishing genera, sections and subsections, as well as related species. In this study, we present the first stigma morphological studies for the most numerous genera from the tribe Orobancheae and this paper may determine features possible to use in solving certain taxonomic problems and evolutionary relationships of the species.

Keywords

flower morphology, gynoecium, Orobanche, Phelipanche, taxonomy

Introduction

Orobanchaceae is the largest parasitic plant family with 102 genera and over 2,100 species (Nickrent 2020). In this family, the tribe Orobancheae is the oldest and most species-rich lineage of holoparasitic Orobanchaceae (McNeal et al. 2013; Schneider and Moore 2017; Piwowarczyk et al. 2021). Due to the strongly reduced vegetative organs of obligate parasitic plants, they belong to the most critical genera of world flora and cause many difficulties and mistakes in species identification. They do not form vegetative organs such as leaves (reduced to simple scales) and their appearance is limited to generative stems with flowers, highly variable in colour and morphology, so any additional characteristics of systematic value would be helpful.

Recently, studies on the molecular phylogeny and taxonomy of Orobanchaceae have clarified many controversial issues (Piwowarczyk et al. 2017, 2018, 2019, 2021 and references therein). The relationships within several important lineages can also be explained by additional morphological analysis. Previous studies on holoparasitic Orobanchaceae seeds and pollen morphology (e.g. Abu Sbaih and Jury 1994; Abu Sbaih et al. 1994; Plaza et al. 2004; Domina and Colombo 2005; Zare et al. 2013; Piwowarczyk 2015; Piwowarczyk et al. 2015, 2016; Zare and Dönmez 2016; Piwowarczyk et al. 2020 and references therein) and petal micromorphology (Piwowarczyk and Kasińska 2017), as well as floral volatile organic compounds (VOC) (Tóth et al. 2016) have proved to be useful as significant complementary sources of taxonomic data.

The stigma is a part of the gynoecium, the female reproductive system of a flower, with an ephemeral and receptive surface of the style that collects the pollen and creates appropriate conditions for its hydration and germination. These female tissues also promote outcrossing or self-fertilisation by the coordinated timing of their maturation with pollen release (Heslop-Harrison 1981; Edlund et al. 2004). Understanding floral morphology is fundamental to evaluating the interactions between pollen grains and the stigmas, as well as for understanding the relationship between flowers and pollinators. Moreover, many species can only be identified by their floral characteristics (Heslop-Harrison 1992). Angiosperm stigmas are structurally very diverse and some families have stigmas of more than one type. However, stigma morphology can be used, similarly to pollen morphology, to assist taxonomic classifications (Heslop-Harrison and Shivanna 1977). The taxonomic importance and the variability of stigmas have been described in both monocotyledonous and dicotyledonous plants at the inter- and intrageneric level in for example, Bromeliaceae (Brown and Gilmartin 1989), Boragineae (Bigazzi and Selvi 2000), Vochysiaceae (Carmo-Oliveira and Morretes 2009), Convolvulaceae (Wright et al. 2011) and Cactaceae (Mosti et al. 2013).

Amongst the Orobanchaceae studied by Heslop-Harrison and Shivanna (1977), Orobanche s.l. presented a dry stigma with unicellular papillae. This group with dry stigmas was characterised by lack of any surface secretion and the subgroups separate into species, based on the presence of trichomes or papillae. A review of available literature showed a scarcity of data describing the morphological variation of Orobancheae stigmas. Teryokhin et al. (1993) studied the morphological differences of the stigmas for about 50 taxa of the Orobanche L. and Phelipanche Pomel genera. The stigmas of the tribe Orobancheae show considerable variation, i.e. often subglobose in Cistanche Hoffmannsegg & Link and usually discoid to subglobose in Phelypaea L. In the Orobanche and Phelipanche genera, the stigmas are 2–4-lobed with varied shape lobes, for example, elongated, spherical, ovate and/or flattened (Kreutz 1995; Teryokhin 1997; Piwowarczyk et al. 2019). Papers on the morphological descriptions of Orobancheae species have focused mainly on the colour and the degree of fusion of the stigma lobes (e.g. Kreutz 1995; Piwowarczyk et al. 2019; Thorogood and Rumsey 2021). Therefore, studies are necessary on the morphological variation and taxonomic significance of stigmas, especially in the case of systematic division or problematic groups of species. In Orobanchaceae, Phelipanche and Orobanche s. str. are the largest holoparasitic genera that comprise ca. 50–62 and 150 species, respectively (Piwowarczyk et al. 2019), which are parasitic on the roots of other vascular plants. These genera are characterised by worldwide distribution, especially in the Mediterranean Basin, western and central Asia, north Africa, while less represented in America and Oceania (alien) (Piwowarczyk et al. 2019, 2021). In this paper, we focused on the Central European area, with only five species in Phelipanche, in contrast to western and central Asia and the Mediterranean, where the genus Orobanche represents the largest genus with about 20–23 representatives (Piwowarczyk et al. 2018).

The present study aimed to evaluate intraspecific, interspecific and intergeneric stigmas variability and then find differences of stigma morphology representatives of the Orobanche and Phelipanche genera from Central Europe using stereomicroscopy and to provide new insights into its potential taxonomic value. One of the primary objectives was to describe the stigma morphology and identify stigma characters, based on qualitative and quantitative data and to evaluate how useful these characteristics are in systematics and diagnostics for the investigated taxa. This paper also focused on selecting the best diagnostic features that could be used for future stigma analysis in the remaining genera and species of Orobanchaceae.

Materials and methods

Plant material

Specimens and samples of stigmas for the present study were observed, collected and photographed by the authors (primarily by Piwowarczyk), mainly during several field trips between 2006 and 2022 in Central Europe (especially Poland, Czech Republic, Slovakia and Austria) and some complementary specimens were also observed from other parts of Europe. A total of 40 samples representing 24 species were analysed (5 Phelipanche and 19 Orobanche), usually from two different localities per species (Table 1). The study was based on fresh and mature specimens collected in the natural habitats and on dry herbarium specimens where mature stigmas were selected from herbarium collections, as well as on plant material which was fixed in FAA (Formalin-Aceto-Alcohol) solution. The fresh specimens were kept in the refrigerator, observed and recorded quickly to avoid dehydration within tens of minutes. Dried flowers, removed from herbarium specimens, were heated to boiling point and left to observe after several minutes. For the purpose of comparison and to eliminate variation that might be caused by sampling from different flower areas, we took mature stigmas close to the middle portion of an inflorescence. In addition, our observations and measurements of stigmas were also compared with numerous photographs of analysed species, as well as with problematic sections, subsections and/or series of species from other parts of Europe and Asia. Our samples have also been presented in recent molecular phylogenetic studies (Piwowarczyk et al. 2018, 2021). The plant names were updated, based on the World Flora Online (WFO) (2022), as well as the Index of Orobanchaceae (Sánchez Pedraja et al. 2016). Vouchers of plant material were deposited in the Herbarium (KTC) of the Institute of Biology, Jan Kochanowski University in Kielce (KTC acronym, according to Thiers 2017). Voucher information and geographic origin are included in Table 1. The terminology of stigma morphology was given according to Heslop-Harrison and Shivanna (1977), Heslop-Harrison (1992), Teryokhin et al. (1993), Kreutz (1995), Teryokhin (1997), Williams (2009), Wright et al. (2011) and Konarska and Chmielewski (2020). Systematic division was adopted according to Beck (1930) and Teryokhin et al. (1993), the scheme followed, explicitly or implicitly, by most researchers and some recent taxonomic changes (McNeill et al. 2012; Piwowarczyk et al. 2017, 2018, 2021).

Table 1.
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Species used in the present study and voucher information.

No Species Voucher Host
1a Orobanche alba Stephan ex Willd. Poland, Kąty II, 15 July 2006, R. Piwowarczyk (KTC) Salvia verticillata L.
1b O. alba Poland, Lasocin, 27 July 2006, R. Piwowarczyk (KTC) S. verticillata
2a O. alsatica Kirschl. Poland, Kielce, Grabina Mt., 19 June 2021, R. Piwowarczyk & K. Ruraż (KTC) Peucedanum cervaria (L.) Lapeyr.
2b O. alsatica Poland, Kąty near Zamość, 15 July 2006, R. Piwowarczyk (KTC) P. cervaria
3 O. artemisiae-campestris Gaudin Czech Republic, Mikulov, 21 June 2014, R. Piwowarczyk (KTC) Artemisia campestris L.
4a O. bartlingii Griseb. Poland, Podzamcze, 22 June 2021, R. Piwowarczyk & K. Ruraż (KTC) Seseli libanotis W.D.J.Koch
4b O. bartlingii Poland, Cząstków, 30 June 2006, R. Piwowarczyk (KTC) S. libanotis
5a O. caryophyllacea Sm. Poland, Kików, 28 May 2021, R. Piwowarczyk & K. Ruraż (KTC) Galium verum L.
5b O. caryophyllacea Poland, Łagiewniki, 13 June 2022, R. Piwowarczyk (KTC) G. mollugo L.
6a O. coerulescens Stephan in Willd. Poland, Pasturka, 28 June 2022, R. Piwowarczyk & K. Ruraż (KTC) A. campestris
6b O. coerulescens Poland, Dobrowoda, 19 June 2010, R. Piwowarczyk (KTC) A. campestris
7 O. cumana Wallr. Ukraine, Kherson, 31 May 2019, R. Piwowarczyk (KTC) Artemisia sp.
8a O. elatior Sutton Poland, Dzierżysław near Kietrz, 11 July 2010, R. Piwowarczyk (KTC) Centaurea scabiosa L.
8b O. elatior Poland, Baldram, 10 July 2010, R. Piwowarczyk (KTC) C. scabiosa
9a O. flava Mart. ex F.W. Schultz Poland, Tatra Mts, Mała Łąka Valley, 25 July 2014, R. Piwowarczyk (KTC) Petasites kablikianus Tausch ex Bercht.
9b O. flava Slovakia, Nizkie Tatra Mts, Ohniste, 4 August 2011, R. Piwowarczyk (KTC) P. kablikianus
10 O. gracilis Sm. Austria, Hundsheim, 21 June 2014, R. Piwowarczyk (KTC) Anthyllis vulneraria L., Dorycnium pentaphyllum subsp. germanicum (Gremli) Gams
11 O. hederae Duby Spain, Elx, palm garden, 28 April 2009, R. Piwowarczyk (KTC) Hedera helix L.
12a O. kochii F.W. Schultz (=O. centaurina Bertol.) Poland, Boria, 4 July 2021, R. Piwowarczyk (KTC) C. scabiosa
12b O. kochii Poland, Pęczelice, Ostra Mt., 7 July 2022, R. Piwowarczyk & K. Ruraż (KTC) C. scabiosa
13 O. lucorum A. Braun ex F.W. Schultz Poland, Warsaw, Botanical Garden, 10 July 2009, R. Piwowarczyk (KTC) Berberis vulgaris L.
14a O. lutea Baumg. Poland, Pęczelice, 28 May 2021, R. Piwowarczyk & K. Ruraż (KTC) Medicago falcata L.
14b O. lutea Poland, Ząbkowice, 29 May 2021, R. Piwowarczyk & K. Ruraż (KTC) M. sativa L.
15a O. mayeri (Suess. & Ronniger) Bertsch & F. Bertsch Poland, Pieniny Mts, Trzy Korony, 30 July 2009, R. Piwowarczyk (KTC) Laserpitium latifolium L.
15b O. mayeri Poland, Pieniny Mts, Białe Skałki, 29 July 2009, R. Piwowarczyk (KTC) L. latifolium
16 O. minor Sm. Poland, Żywiec, 19 July 2009, R. Piwowarczyk (KTC) Trifolium repens L.
17a O. picridis F. W. Schultz Poland, Pińczów, 28 June 2022, R. Piwowarczyk & K. Ruraż (KTC) Picris hieracioides L.
17b O. picridis Poland, Pęczelice, Ostra Mt., 7 July 2022, R. Piwowarczyk & K. Ruraż (KTC) P. hieracioides
18a O. reticulata Wallr. Lubiatowo, June 2014, R. Piwowarczyk (KTC) Cirsium arvense (L.) Scop.
18b O. reticulata Slovakia, Nizkie Tatra Mts, Ohiste, 4 August 2011, R. Piwowarczyk (KTC) Carduus defloratus L.
19 O. teucrii Holandre Austria, Hundsheim, 20 June 2014, R. Piwowarczyk (KTC) Teucrium montanum L.
20a Phelipanche arenaria (Borkh.) Pomel Czech Republic, Mikulov, 21 June 2014, R. Piwowarczyk (KTC) A. campestris
20b P. arenaria Poland, Młyny, 28 June 2022, R. Piwowarczyk & K. Ruraż (KTC) A. campestris
20c P. arenaria Poland, Pasturka, 28 June 2022, R. Piwowarczyk & K. Ruraż (KTC) A. campestris
20d P. arenaria Poland, Zwierzyniec, 29 June 2021, R. Piwowarczyk & K. Ruraż (KTC) A. campestris
21 P. bohemica (Čelak.) Holub Poland, Zawiercie, 11 July 2010, R. Piwowarczyk (KTC) A. campestris
22 P. caesia (Rchb.) Soják Ukraine, Askania Nova, 16 June 2011, R. Piwowarczyk (KTC) A. austriaca Jacq.
23 P. purpurea (Jacq.) Soják Poland, Chrzanów, 18 June 2009, R. Piwowarczyk (KTC) Achillea millefolium L.
24a P. ramosa (L.) Pomel Poland, Brzeziny, 4 September 2021, R. Piwowarczyk & K. Ruraż (KTC) Nicotiana tabacum L.
24b P. ramosa Poland, Szewce, 15 September 2013, R. Piwowarczyk (KTC) Solanum lycopersicum L.

Morphometric analysis

Twenty-one quantitative and qualitative morphological features were measured. Sixteen quantitative features were analysed in the bottom view, i.e. the length of 2-lobed stigma (typical) (A) (µm), the length of single lobes (A1, A2) (µm), the length of upper separation in the middle part between lobes (B) (µm), the length of lower separation in the middle part between lobes (C) (µm), the length of the mouth of the stylar canal (slit) (D) (µm), the width of single lobes (E1, E2) (µm), the width in the middle part of the stigma (F) (µm), the area of 2-lobed stigma (G) (µm2), the area of single lobes (G1, G2) (µm2), the angle between 2-lobed stigma in the upper part (H) (°) and the angle between 2-lobed stigma in the lower part (I) (°). In the front view, two morphological features were examined, i.e. the length of 2-lobed stigma (J) (µm) and the area of 2-lobed stigma (µm2) (K) (Fig. 1). Additionally, five qualitative features, namely type, subtype, shape (in bottom view), colour and the degree of stigma lobes separation were taken into account for the morphological analysis of the stigmas.

Figure 1. 

Measurement scheme of a 2-lobed stigma of Orobanche. A–I bottom view J, K front view A the length of 2-lobed stigma (µm) A1, A2 the length of single lobes (µm) B the length of upper separation in the middle part between lobes (µm) C the length of lower separation in the middle part between lobes (µm) D the length of the mouth of the stylar canal (slit) (µm) E1, E2 the width of single lobes (µm) F the width in the middle part of the stigma (µm) G the area of 2-lobed stigma (µm2) G1, G2 the area of single lobes (µm2) H the angle between 2-lobed stigma in the upper part (°) I the angle between 2-lobed stigma in the lower part (°) J the length of 2-lobed stigma (µm) K the area of 2-lobed stigma (µm2).

Morphological observations of the stigmas were carried out using a Nikon SMZ-800 stereoscopic microscope coupled with a NIKON DSFi3 camera (Tokyo, Japan). Measurements were made using AxioVision SE64 Rel. 4.9.1 software (Carl Zeiss, Germany). For morphological characterisation, 30–50 stigmas of mature flowers from 5–10 randomly selected individuals of each sample of species were used. Data analyses were performed using Statistica 13 (TIBCO Software Inc. 2017). Eleven quantitative and two qualitative characters of stigmas were analysed using UPGMA, i.e. the length of 2-lobed stigma (typical) (A) (µm), the length of upper separation in the middle part between lobes (B) (µm), the length of lower separation in the middle part between lobes (C) (µm), the width of single lobes (E1, E2) (µm), the width in the middle part of the stigma (F) (µm), the area of 2-lobed stigma (G) (µm2), the angle between 2-lobed stigma in the upper part (H) (°), the angle between 2-lobed stigma in the lower part (I) (°), the length of 2-lobed stigma (J) (µm) and the area of 2-lobed stigma (µm2) (K), as well as the type and subtype of the stigma. These features were chosen because they showed the differences and similarities between species. A dendrogram was prepared, based on the similarity matrix generated using Gower’s general similarity coefficient (Gower 1966). Both analyses were performed using the MVSP package version 3.1 (Kovach 1999).

Results

General characteristics of stigma

Morphological characterisation of the stigmas of Orobanche and Phelipanche has provided important data for the taxonomy of Orobancheae. The study showed some morphological similarities in stigma characters in both genera, for example, stigma usually 2-lobed, occasionally 3- and 4-lobed, lobes spherical to ovulate in shape (Fig. 2). The third lobe may be centrally located between the two lobes or directly under one of the lobes (Figs 2C, D). The centrally narrowed stigma was bent towards the lower lip and in the middle part was described by the presence of the mouth of the stylar canal. The stigma was covered with numerous papillae concentrated on the coloured lobes that were regularly arranged. The bow-shaped stigma had a viscous substance on the surface at the receptive stage. In buds, the length of the mouth of the stylar canal (slit) was more visible because it did not contain this substance.

Figure 2. 

Micrographs of typical 2-lobed stigmas of Orobanche and Phelipanche and occasional 3-lobed stigmas of Orobanche. A Orobanche B Phelipanche C, D 3-lobed stigmas of Orobanche. Scale bars: 1000 µm (A, C, D); 500 µm (B). Phot. K. Ruraż, J. Posłowska and K. Zubek.

Orobanche

The stigmas of Orobanche were hemispherical, spherical, rounded, rarely oval. These stigmas were varied in colour from white, yellow, orange, pink, purple, red to dark brown with partially fused or separated lobes (Table 2, Figs 2A, 3A–P, 4A–F). In the field research, two forms were observed in Orobanche, euchrome (normal colour) and hypochromic (yellow), which were easy to distinguish. We observed that the hypochromic form was smaller than the euchromic in each feature tested.

Table 2.
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The comparison of the stigmas of selected species of Orobanche and Phelipanche.

No Species The length of 2-lobed stigma (A) (µm) The length of single lobes (A1) (µm) The length of single lobes (A2) (µm) The length of upper separation in the middle part between lobes (B) (µm) The length of lower separation in the middle part between lobes (C) (µm) The length of the mouth of the stylar canal (slit) (D) (µm) The width of single lobes (E1) (µm) The width of single lobes (E2) (µm) The width in the middle part of the stigma (F) (µm) The area of 2-lobed stigma (G) (µm2) The area of single lobes (G1) (µm2) The area of single lobes (G2) (µm2) The angle between 2-lobed stigma in the upper part (H) (˚) The angle between 2-lobed stigma in the lower part (I) (˚) The length of 2-lobed stigma (J) (µm) The area of 2-lobed stigma (µm2) (K) Type Subtype Shape Colour Degree of stigma lobes separation
Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max Min Mean Max
1a Orobanche alba 2406 2733 2956 1042 1267 1398 1053 1291 1420 250 400 436 175 322 390 850 1230 1420 1123 1334 1520 950 1183 1326 556 600 635 2757642 2850613 3000677 1245823 1324428 1445236 1123574 1249113 1445834 100 159 168 100 125 138 2553 2725 2953 1645762 1751163 1863425 2 4 5 dark red or purple (rarely yellow or orange) 2
1b O. alba 2654 2769 3096 1095 1292 1423 1111 1263 1452 243 411 452 200 310 350 876 1249 1390 1002 1367 1457 1136 1156 1383 503 547 620 2651752 2977262 3100111 1235426 1383402 1445783 1124735 1242331 1445238 120 154 160 112 124 135 2389 2560 2756 1594525 1725078 1852642 2 4 5 dark red or purple (rarely yellow or orange) 2
2a O. alsatica 2770 3263 3376 1258 1389 1506 1253 1394 1524 150 320 353 380 503 563 1255 1513 2024 1518 1725 1882 1534 1763 2044 713 1029 1217 2949725 4223848 5073149 1350001 1895292 2049205 1351501 1825268 2211640 106 121 149 90 99 142 2497 3155 3409 2003320 3070327 3438793 2 7 8 yellow 4
2b O. alsatica 2776 3283 3423 1280 1390 1574 1289 1468 1600 152 331 362 385 502 559 1302 1513 2083 1552 1726 1889 1542 1765 2022 723 1168 1227 2952681 4234639 5045267 1345856 1864142 2057257 1325423 1948092 2354521 110 119 152 95 98 140 2500 3119 3375 2052425 3072867 3524578 2 7 8 yellow 4
3 O. artemisiae-campestris 2343 2489 2635 1055 1112 1169 824 848 872 269 294 318 305 308 333 952 1200 1425 1315 1435 1655 1296 1436 1481 736 862 988 2632733 2961322 3289911 1346029 1494916 1643804 1163778 1289765 1415751 110 117 125 115 127 140 2458 2559 2715 1405555 1625555 2025555 2 5 6 pink, purple-brownish, reddish 1
4a O. bartlingii 2908 3289 3525 1324 1435 1649 1322 1440 1598 156 377 560 492 643 932 1415 1759 2136 1639 1754 1974 1453 1802 2128 625 850 976 3179984 4461832 5803293 1549428 2254127 2458532 1581602 2208461 2859009 97 118 152 36 62 96 3070 3222 3743 2789644 3172420 3854744 2 7 8 yellow 4
4b O. bartlingii 3122 3290 3452 1352 1395 1658 1222 1352 1485 157 363 580 482 596 935 1423 1668 2098 1652 1796 1985 1425 1782 2119 636 846 998 3175235 4265832 5795423 1484526 2095321 2394258 1535275 2092462 2852954 95 123 155 40 68 90 3100 3207 3658 2758452 3157156 3792542 2 7 8 yellow 4
5a O. caryophyllacea 2625 3234 4135 1174 1420 1814 1107 1411 1833 163 263 397 248 423 769 1307 1735 2150 1321 1644 1805 1356 1689 1925 546 899 1122 2952876 4194741 5952683 1495078 2133317 2856202 1067414 2118599 2998225 108 134 148 93 116 148 2542 3173 4003 2214881 3103345 3929173 2 6 7 dark brown, purple or rarely yellow or orange 5
5b O. caryophyllacea 2717 3240 3857 1193 1431 1666 1149 1423 1714 162 257 325 253 436 685 1322 1753 2221 1504 1612 1871 1197 1607 1920 702 887 1047 2235708 4133380 5403435 1788448 2094521 2647715 1463544 2091128 2558874 123 139 146 102 116 146 3085 3160 3576 2902541 3125328 3968729 2 6 7 dark brown, purple or rarely yellow or orange 5
6a O. coerulescens 2045 2280 2602 862 988 1047 821 939 1011 172 240 272 175 250 399 729 888 1143 849 1257 1588 823 1307 1652 637 979 1200 1545257 2107260 2763040 536064 633490 733232 453078 688153 753521 133 141 151 112 122 143 1667 2019 2455 785340 1105242 1235242 2 2 3 white to yellowish-white, rarely bluish 3
6b O. coerulescens 2044 2270 2636 821 900 1100 850 990 1112 180 250 280 178 240 301 740 890 1200 870 1200 1600 840 1310 1700 650 999 1210 1586422 2108452 2794224 552222 654222 745252 475525 702541 765421 138 150 160 125 120 152 1600 2000 2389 796655 1100055 1245522 2 2 3 white to yellowish-white, rarely bluish 3
7 O. cumana 2191 2299 2600 650 950 1040 800 980 1200 195 243 290 190 247 325 790 952 1212 888 1215 1650 860 1325 1725 690 999 1242 1725555 2249511 2800502 652224 802121 1052555 681242 855521 104855 140 158 171 130 122 160 1600 2124 2544 799222 1255250 1352420 2 2 3 white to yellowish-white, rarely bluish 3
8a O. elatior 2211 2750 3022 902 1200 1425 980 1192 1422 150 254 380 150 280 360 1100 1302 1380 1400 1500 1630 1182 1450 1690 782 1020 1098 2452252 3182522 3852424 1252522 1620222 1882522 1258522 1605525 1952522 125 138 150 110 130 140 2345 2685 3089 1555252 1922525 2742252 2 7 8 yellow 4
8b O. elatior 2279 2665 3002 1040 1182 1402 1055 1182 1423 182 256 460 228 293 378 1120 1305 1450 1405 1520 1650 1252 1420 1752 800 1025 1100 2575255 3152522 3825551 1425254 1622252 1982522 1182525 1625444 1982202 118 140 162 115 128 153 2300 2688 3099 1505557 1922442 2654444 2 7 8 yellow 4
9a O. flava 2440 3052 3325 1161 1339 1520 1026 1313 1455 182 222 253 215 339 441 1133 1441 1567 987 1308 1441 1045 1383 1414 564 787 958 2177820 3201648 3542524 1125475 1510172 1791079 1104524 1474925 1785244 136 147 158 122 135 149 3113 3431 4002 2954225 3182604 3525452 2 7 8 yellow, rarely orange 4
9b O. flava 2480 3143 3389 1200 1400 1543 1130 1380 1487 185 227 260 220 340 448 1150 1482 1579 995 1358 1482 1096 1399 1487 568 790 987 2198525 3235255 3575225 1142524 1545722 1800241 1132522 1502142 1802141 139 149 159 125 137 149 3131 3458 4025 2982201 3325214 3685224 2 7 8 yellow, rarely orange 4
10 O. gracilis 3200 4091 4522 1523 1777 1952 1452 1569 1852 290 300 315 520 555 575 1950 2130 2300 950 1031 1100 1000 1083 1120 590 650 720 3352752 3836796 4525252 1524586 1891079 2152354 1535752 1839782 2165242 115 120 129 120 142 150 3522 4145 4522 3952435 4722574 5054242 2 3 4 yellow lobes with a reddish base of the stigma to the style tip 5
11 O. hederae 2316 2457 2620 1021 1114 1350 1034 1152 1250 250 300 400 270 310 410 1100 1200 1420 1242 1473 1652 1288 1499 1700 818 881 1002 2722202 3049217 3952542 1259925 1418678 1602020 1252522 1421152 1625521 105 125 130 98 114 125 2225 2418 2701 1425256 1686525 1915252 2 5 6 yellow 1
12a O. kochii 2133 2657 2957 878 1190 1361 965 1174 1355 146 241 371 145 281 352 1071 1227 1334 1370 1503 1626 1131 1402 1669 751 1005 1063 2273587 3119816 3638828 1173520 1569933 1787545 1190538 1526655 1847662 116 134 149 103 126 138 2300 2616 3013 1548757 1903199 2612049 2 7 8 yellow 4
12b O. kochii 2271 2682 2986 1034 1160 1347 1024 1140 1368 174 242 455 226 292 373 1098 1238 1421 1376 1507 1646 1211 1445 1731 794 1002 1094 2397616 3135407 3657502 1324292 1501738 1917114 1043585 1500763 1906603 108 130 155 110 124 152 2282 2605 3058 1445172 1905557 2580093 2 7 8 yellow 4
13 O. lucorum 2289 2885 3158 1025 1205 1325 885 1210 1299 157 205 234 189 302 407 995 1301 1358 887 1184 1275 884 1170 1247 480 687 862 2085214 3098547 3352524 1052442 1395241 1675252 1042252 1395241 1685221 128 140 148 115 129 141 2958 3258 3842 2752514 2958541 3295255 2 7 8 yellow 4
14a O. lutea 2414 3213 3425 978 1251 1587 1124 1244 1509 207 261 321 313 434 555 1057 1406 1745 1368 1608 2031 1342 1624 1939 816 999 1232 3079257 4167377 5275009 1413468 2076596 2643138 1599790 2080971 2590285 116 133 144 78 119 135 2603 3075 3198 2506590 3062143 3355113 2 6 7 yellow, rarely orange 5
14b O. lutea 2631 3252 3489 1158 1375 1721 1159 1358 1523 229 261 440 332 432 875 1091 1461 1869 1512 1675 2125 1616 1654 2010 820 989 1337 3134725 4177720 5565740 1540919 2167075 3080438 1607626 2150782 2816204 121 134 152 103 119 137 2690 3043 3363 2800458 3083820 3481223 2 6 7 yellow, rarely orange 5
15a O. mayeri 2367 3024 3214 1124 1330 1501 1015 1301 1424 179 220 249 200 328 420 1086 1375 1499 979 1289 1399 999 1299 1400 524 775 942 2154424 3195242 3495521 1115471 1492201 1720214 1094254 1452142 1755288 129 138 147 120 130 145 3107 3401 3952 2884252 3125415 3452542 2 7 8 yellow 4
15b O. mayeri 2380 2999 3203 1100 1289 1498 999 1299 1387 168 215 245 198 319 415 1079 1365 1487 968 1276 1384 990 1257 1397 517 768 935 2150254 3185143 3472514 1117524 1485214 1745241 1092514 1442252 1739541 130 142 149 119 132 144 3095 3398 3925 2895310 3099604 3385145 2 7 8 yellow 4
16 O. minor 2027 2333 2632 813 999 1113 804 987 1195 213 253 329 261 299 361 1023 1204 1423 1121 1315 1505 1176 1303 1596 577 737 923 1875234 2524575 3278563 956424 1240557 1575224 974255 1234452 1654224 109 124 139 95 114 119 2324 2499 2799 1425775 1635554 1835447 2 5 6 pinkish, reddish or purplish rarely white 1
17a O. picridis 2039 2341 2748 796 996 1150 864 1029 1217 233 277 318 270 308 370 1175 1244 1480 1187 1372 1541 1200 1349 1470 732 800 952 2020061 2562134 3416204 904198 1264524 1627401 968520 1284620 1677785 107 123 132 98 114 121 2157 2525 2760 1420156 1687767 1853354 2 5 6 purple, dark red and pink 1
17b O. picridis 2035 2333 2774 824 1004 1207 814 993 1208 249 273 339 270 292 371 1056 1201 1448 1157 1335 1542 1181 1339 1608 543 746 935 1890329 2539792 3313251 980526 1261885 1653207 992278 1250536 1731908 114 123 135 100 116 121 2392 2515 2890 1485242 1674790 1925422 2 5 6 purple, dark red and pink 1
18a O. reticulata 2200 2459 2852 1050 1280 1400 1060 1270 1452 270 442 471 154 315 382 866 1249 1423 1245 1408 1555 995 1185 1324 570 603 645 2452534 2635921 2885422 1305424 1422813 1495242 1132531 1258456 1432574 123 150 161 92 122 140 2123 2582 2952 1782243 2023996 2174252 2 4 5 brownish or purplish as well as usually lighter in the upper part of the stigma 2
18b O. reticulata 2300 2560 2962 1105 1315 1458 1110 1305 1482 275 445 478 156 320 385 876 1286 1487 1287 1458 1599 999 1198 1357 585 624 657 2475254 2668541 2895252 1312524 1432421 1502241 1272221 1475214 1562221 125 155 165 97 125 144 2157 2593 2999 1824224 2162437 2302552 2 4 5 brownish or purplish as well as usually lighter in the upper part of the stigma 2
19 O. teucrii 2617 3259 3935 1166 1339 1779 1100 1326 1756 160 230 366 250 430 770 1250 1600 1950 1258 1671 1752 1295 1679 1885 560 885 1085 2923211 4188569 5325321 1402542 1922681 2795212 1402674 1954136 2752642 111 140 150 95 117 152 2354 3075 3885 2256413 3188246 3954254 2 6 7 dark brown, purple 5
20a Phelipanche arenaria 1880 2123 2397 785 824 1086 699 712 1023 185 192 295 151 327 368 402 432 616 1210 1480 1802 1250 1458 1704 621 851 977 2489552 2669838 3547202 1220672 1311531 1807843 1039657 1287672 1523739 120 125 134 107 127 154 2000 2183 2288 1415852 1679817 1865272 1 1 1 white 4
20b P. arenaria 1866 2117 2360 824 947 1087 787 904 1055 191 237 309 124 279 350 514 623 804 1178 1448 1750 1258 1484 1714 764 864 999 2143661 2590398 3836144 1057719 1226497 1520612 1052145 1291165 1589813 117 125 133 120 139 154 1954 2000 2235 1405527 1657854 1852727 1 1 1 white 4
20c P. arenaria 1960 2158 2443 870 1048 1121 796 959 1130 202 301 345 148 326 362 436 552 617 1238 1667 1962 1414 1673 1779 851 1010 1237 2752426 3521283 4052127 1224027 1712603 2042492 1126734 1535574 1649937 106 126 120 103 119 152 1888 1940 2135 1385424 1635680 1814525 1 1 1 white 4
20d P. arenaria 1858 2181 2314 847 982 1112 711 901 1033 201 250 310 110 304 344 485 570 669 1338 1661 1803 1288 1617 1737 830 950 1098 2652524 2951856 3524525 1096897 1303751 1679465 894185 1194634 1460135 112 120 128 120 120 156 1856 1936 2099 1395472 1636061 1825577 1 1 1 white 4
21 P. bohemica 2089 2250 2500 987 1000 1083 869 1005 1183 240 252 263 202 242 337 558 622 640 1452 1570 1700 1476 1558 1602 974 1020 1128 2825152 3129718 3352525 1152525 1385251 1539616 1152555 1395225 1532525 119 125 130 111 108 121 1958 1999 2102 1502252 1702555 1842522 1 1 1 yellow-white 4
22 P. caesia 2059 2188 2400 929 961 999 948 974 986 300 305 306 286 310 389 500 515 635 1500 1702 1800 1519 1610 1700 890 900 918 3118762 3156066 3222055 1322021 1481583 1746409 1382380 1400571 1565378 110 129 140 107 116 120 1920 2065 2255 1385242 1654332 1834555 1 1 1 white 4
23 P. purpurea 2056 2219 2312 865 966 980 859 991 1156 230 242 250 190 205 328 552 602 620 1435 1462 1684 1452 1512 1598 950 1015 1114 2602565 2818684 3030555 1001678 1293136 1495412 1004524 1277624 1357524 100 119 125 101 108 120 1923 1983 2025 1496874 1739657 1836524 1 1 1 white or pale blue or violet 4
24a P. ramosa 1159 1520 1670 481 673 717 469 565 621 163 198 226 200 236 315 312 367 477 811 1023 1113 814 979 1099 413 555 696 991449 1400737 1679621 332470 591670 759460 329541 586839 765428 82 101 116 99 108 118 1052 1288 1412 365241 449118 589117 1 1 2 white or bright bluish, rarely yellowish 4
24b P. ramosa 1269 1568 1700 446 708 754 485 623 645 169 220 264 206 277 317 327 423 486 947 1206 1274 823 1165 1274 510 661 766 996252 1647702 1893740 369303 755309 845729 365225 708890 849552 78 94 106 90 101 112 1110 1323 1500 394527 487236 575272 1 1 2 white or bright bluish, rarely yellowish 4

Explanations: stigma type: 1–oval, rarely hemispherical, most often white, rare light blue or violet and yellow and lobes separated; 2–spherical, hemispherical, rounded, rarely oval, multi-coloured: white, yellow, orange, pink, purple, red to dark brown with partially fused or separated lobes; stigma subtype (in bottom view): 1–oval, rarely hemispherical, most often white, rare light blue or violet and yellow, lobes separated; 2–hemispherical, rarely rounded, white to yellowish-white, rarely bluish, lobes partially separated; 3–hemispherical to rounded, lobes distinctly separated; 4–spherical to rounded, multi-coloured, lobes in closer proximity; 5–hemispherical, multi-coloured, lobes in closer proximity or even partially united; 6–hemispherical to oval, multi-coloured, lobes distinctly separated; 7–hemispherical rarely oval, yellow, lobes separated; stigma shape (in bottom view): 1–oval, rarely hemispherical; 2–oval to hemispherical; 3–hemispherical, rarely rounded; 4–hemispherical to rounded; 5–spherical to rounded; 6–hemispherical; 7–hemispherical to oval; 8–hemispherical, rarely oval; degree of stigma lobes separation (in front view):1–closer proximity or even partially united; 2–closer proximity; 3–partially separated; 4–separated; 5–distinctly separated.

The stigmas of O. alsatica, O. bartlingii, O. elatior, O. flava, O. kochii, O. lucorum and O. mayeri belonging to the subsect. Curvatae (Beck) Piwow., Ó. Sánchez & Moreno Mor. consisted of two usually yellow lobes (in O. flava also orange lobes) which were hemispherical, rarely oval in shape and were separated (Table 2, Figs 3C–H, 4A, B, D). The UPGMA analysis on the basis of given features distinguished three subgroups: the first one included O. alsatica and O. bartlingii, the second was represented by O. elatior and O. kochii and the third by O. flava, O. lucorum and O. mayeri (Fig. 5). The analysed samples of O. alsatica and O. bartlingii were in a very close relationship and represented O. alsatica aggr. which is a problematic complex. In O. bartlingii, the shape of the mouth of the stylar canal (slit) was more irregular than O. alsatica. A visible difference in shape between species was marked between the lobes in the lower part and there was a larger separation in O. bartlingii. The stigmas in the front view in O. bartlingii were more pronounced and marked than in O. alsatica, which appear more flattened (Figs 4A1, B1). The length of 2-lobed stigma (A, J) of the first subgroup fell within a range of (2770–)3281(–3525) μm and (2497–)3176(–3743) μm, with an area (G, K) varying between (2949725–)4296538(–5803293) μm2 and (2003320–)3118193(–3854744) μm2. The width of single lobes (E1, E2) fell into a range of (1518–)1750(–1985) μm and (1425–)1778(–2128) μm, while the width in the middle part of the stigma (F) varied within a range of (625–)973(–1227) μm. The length of upper and lower separation in the middle part between lobes (B, C) was in a range of (150–)348(–580) μm and (380–)561(–935) μm and the angle between 2-lobed stigma in the upper and lower part (H, I), comprised (95–)120(–155)° and (36–)82(–142)° (Table 2, Fig. 6). In addition, the second and third subgroups were more similar, based on analysed features of stigmas to the previous one. The length of 2-lobed stigma (A, J) of the second subgroup (represented by O. elatior and O. kochii) comprised (2133–)2689(–3022) μm vs. (2289–)3021(–3389) and (2282–)2649(–3099) μm vs. (2958–)3389(–4025), with an area (G, K) equal to (2273587–)3147567(–3852424) μm2 vs. (2085214–)3183167(–3575225) μm2 and (1445172–)1913431(–2742252) μm2 vs. (2752514–)3138276(–3685224) μm2. In the second subgroup, the width of single lobes (E1, E2) varied between (1370–)1508(–1650) μm and (1131–)1429(–1752) μm and in the third (O. flava, O. lucorum and O. mayeri) varied in a range of (887–)1283(–1482) μm and (884–)1302(–1487) μm with the width in the middle part of the stigma (F) falling into a range of (751–)1013(–1100) μm vs. (480–)761(–987) μm. The length of upper and lower separation in the middle part between lobes (B, C) comprised (146–)248(–460) μm and (145–)287(–378) μm for O. elatior and O. kochii and (157–)218(–260) μm and (189–)323(–448) μm for O. flava, O. lucorum and O. mayeri. Finally, the angle between 2-lobed stigma in the upper and lower part (H, I) fell into a range of (108–)136(–162)° vs. (128–)143(–159)° and (103–)127(–153)° vs. (115–)133(–149)° (Table 2, Fig. 6).

Figure 3. 

General habit of selecting flowers of Orobanchaceae species with a stigma in the front view. A Orobanche alba B O. reticulata C O. alsatica D O. bartlingii E O. kochii F O. elatior G O. flava H O. mayeri I O. caryophyllacea J O. teucrii K O. lutea L O. gracilis M O. minor N O. picridis O O. coerulescens P O. cumana R Phelipanche arenaria S P. caesia T P. purpurea U P. ramosa. Phot. R. Piwowarczyk.

Figure 4. 

Micrographs of selected stigmas of the studied species. A Orobanche alsatica B O. bartlingii C O. caryophyllacea D O. kochii E O. lutea F O. picridis G Phelipanche arenaria H P. ramosa. 1 front view 2 bottom view 3 lateral view 4 back view. Scale bars: 1000 µm (A1–A3, B1–C4, D3, E1–E4, G1, G3); 500 µm (A4, D1, D2, D4, F1–F4, G2, G4, H3); 100 µm (H1, H2, H4). Phot. K. Ruraż, J. Posłowska and K. Zubek.

Figure 5. 

UPGMA dendrogram of morphological differentiation of Orobanchaceae stigmas.

Figure 6. 

Box and whisker plots of quantitative morphological characters of Orobanchaceae stigmas. Points indicate the mean values (open square), boxes represent 25 and 75% percentiles and range (whiskers) represent 1 and 99% percentiles. Numbers indicate examined species (Table 2).

Orobanche coerulescens and O. cumana from the sect. Inflatae (subsect. Inflatae sensu Beck) consisted mostly of hemispherical, rarely rounded stigmas with two lobes which were white to yellowish-white, rarely bluish and partially separated (Table 2, Figs 3O, P). These species represented some of the smallest stigmas of the genus Orobanche that were analysed, i.e. (2044–)2283(–2636) μm and (1600–)2048(–2544) μm in the length of 2-lobed stigma (A, J) with an area (G, K) of (1545257–)2155074(–2800502) μm2 and (785340–)1153516(–1352420) μm2. The width of single lobes (E1, E2) comprised (849–)1224(–1650) μm and (823–)1314(–1725) μm, as well as the width in the middle part of the stigma (F) varied between (637–)992(–1242) μm. The length of upper and lower separation in the middle part between lobes (B, C) fell into a range of (172–)244(–290) μm and (175–)246(–399) μm and the angle between 2-lobed stigma in the upper and lower part (H, I) fell into a range of (133–)150(–171)° and (112–)121(–160)° (Table 2, Fig. 6).

Orobanche gracilis from the subsect. Cruentae Teryokhin had hemispherical to rounded and distinctly separated stigmas with two yellow lobes and with a reddish base of the stigmas to the style tip (Table 2, Fig. 3L). The length of 2-lobed stigma (A, J) was the largest of all Orobanchaceae stigmas tested, comprising (3200–)4091(–4522) μm and (3522–)4145(–4522) μm with an area (G, K) varying between (3352752–)3836796(–4525252) μm2 and (3952435–)4722574(–5054242) μm2. The width of single lobes (E1, E2) fell into a range of (950–)1031(–1100) μm and (1000–)1083(–1120) μm and the width in the middle part of the stigma (F) was equal to (590–)650(–720) μm. The length of upper and lower separation in the middle part between lobes (B, C) fell within a range of (290–)300(–315) μm and (520–)555(–575) μm and the angle between 2-lobed stigma in the upper and lower part (H, I) fell into a range of (115–)120(–129)° and (120–)142(–150)° (Table 2, Fig. 6).

Orobanche caryophyllacea, O. lutea and O. teucrii, which are represented in the O. subsect. Orobanche (subsect. Galeatae sensu Teryokhin) had two hemispherical to oval and distinctly separated stigma lobes. The stigmas in O. caryophyllacea and O. teucrii had similar colours, namely dark brown, purple, rarely yellow or orange (in O. caryophyllacea), in contrast to O. lutea which were yellowish, rarely orange (Table 2, Figs 3I–K, 4C, E). Orobanche caryophyllacea and O. teucrii stigmas were similar in terms of the analysis of qualitative and quantitative features, in contrast to O. lutea (Fig. 5). The length of 2-lobed stigma (A, J) of O. caryophyllacea and O. teucrii fell within a range of (2617–)3244(–4135) μm vs. (2414–)3233(–3489) and (2354–)3136(–4003) μm vs. (2603–)3059(–3363), with an area (G, K) varying between (2235708–)4172230(–5952683) μm2 vs. (3079257–)4172549(–5565740) μm2 and (2214881–)3138973(–3968729) μm2 vs. (2506590–)3072982(–3481223) μm2. In O. caryophyllacea and O. teucrii, the width of single lobes (E1, E2) comprised (1258–)1642(–1871) μm and (1197–)1658(–1925) μm, while in O. lutea displayed a range of (1368–)1642(–2125) μm and (1342–)1639(–2010) μm, with the width in the middle part of the stigma (F) in a range of (546–)890(–1122) μm vs. (816–)994(–1337) μm. The length of upper and lower separation in the middle part between lobes (B, C) was (160–)250(–397) μm and (248–)430(–770) μm for O. caryophyllacea and O. teucrii in comparison to (207–)261(–440) μm and (313–)433(–875) μm recorded in O. lutea. The angle between 2-lobed stigma in the upper and lower part (H, I) was equal to (108–)138(–150)° vs. (116–)134(–152)° and (93–)116(–152)° vs. (78–)119(–137)° (Table 2, Fig. 6).

The stigmas of species belonging to the subsect. Glandulosae (Beck) Teryokhin i.e. O. alba and O. reticulata consisted of two spherical to rounded lobes with different colours in closer proximity (Table 2, Figs 3A, B). Orobanche reticulata had more elongated and flattened stigmas with more separated lobes than O. alba, whose stigmas were dark red or purple (rarely yellow or orange), unlike O. reticulata which were brownish or purplish (mostly lighter in the upper part). The length of 2-lobed stigma (A, J) varied within limits of (2200–)2630(–3096) μm and (2123–)2615(–2999) μm with an area (G, K) falling within a range of (2452534–)2783084(–3100111) μm2 and (1594525–)1915669(–2302552) μm2. The width of single lobes (E1, E2) comprised (1002–)1392(–1599) μm and (950–)1181(–1383) μm, as well as the width in the middle part of the stigma (F) was equal to (503–)594(–657) μm. The length of upper and lower separation in the middle part between lobes (B, C) fell within a range of (243–)425(–478) μm and (154–)317(–390) μm and the angle between 2-lobed stigma in the upper and lower part (H, I) fell into a range of (100–)155(–168)° and (92–)124(–144)° (Table 2, Fig. 6).

Species from the subsect. Minores Teryokhin (incl. O. hederae from the subsect. Hederae Teryokhin) (O. artemisiae-campestris, O. hederae, O. minor and O. picridis) had two hemispherical lobes of the stigmas in closer proximity or even partially united. Orobanche minor stigmas varied in colour from pinkish, reddish or purplish to rarely white, similar to O. artemisiae-campestris which were pink, purple-brownish, reddish and O. picridis with purple, dark red and pink lobes and unlike O. hederae which were usually yellow. The distinguishing feature of the stigmas of this group was the presence of a well-developed and convex surface in relation to the base of the stigmas (Table 2, Figs 3M, N, 4F). The UPGMA analysis on the basis of given features distinguished two subgroups, i.e. the first one included O. artemisiae-campestris and O. hederae and the second was represented by O. minor and O. picridis (Fig. 5). The length of 2-lobed stigma (A, J) of the first subgroup was equal to (2316–)2473(–2635) μm vs. (2027–)2336(–2774) and (2225–)2489(–2715) μm vs. (2157–)2513(–2890), with an area (G, K) varying within limits of (2632733–)3005270(–3952542) μm2 vs. (1875234–)2542167(–3416204) μm2 and (1405555–)1656040(–2025555) μm2 vs. (1420156–)1666037(–1925422) μm2. In the first subgroup, the width of single lobes (E1, E2) varied between (1242–)1454(–1655) μm and (1288–)1468(–1700) μm and, in the second, varied in a range of (1121–)1341(–1542) μm and (1176–)1330(–1608) μm, with the width in the middle part of the stigma (F) in a range of (736–)872(–1002) μm vs. (543–)761(–952) μm. The length of upper and lower separation in the middle part between lobes (B, C) was (250–)297(–400) μm and (270–)309(–410) μm for O. artemisiae-campestris and O. hederae in comparison to (213–)268(–339) μm and (261–)300 (–371) μm recorded in O. minor and O. picridis. The angle between 2-lobed stigma in the upper and lower part (H, I) was in a range of (105–)121(–130)° vs. (107–)123(–139)° and (98–)121(–140)° vs. (95–)115(–121)° (Table 2, Fig. 6).

Phelipanche

The stigmas were oval, rarely hemispherical, with separated lobes and were most often white, rarely light blue, violet and yellow (Table 2, Figs 2B, 3R–U, 4G, H). Stigmas are less varied and smaller in size than in Orobanche.

The stigmas of Phelipanche arenaria, P. bohemica, P. caesia and P. purpurea belonging to the sect. Trionychon (Wallr.) Piwow. & Ó. Sánchez (sect. Arenariae Teryokhin) consisted of two white lobes which were oval, rarely hemispherical with clearly separated lobes. Most often they were white, less often light blue or violet and yellow (Table 2, Figs 3R–T, 4G). Measurable data and UPGMA analysis showed the presence of two subgroups P. arenaria and P. caesia in the first, with the second represented by P. bohemica and P. purpurea (Fig. 5). The length of 2-lobed stigma (A, J) of the first subgroup comprised (1858–)2153(–2443) μm vs. (2056–)2235(–2500) and (1856–)2025(–2288) μm vs. (1923–)1991(–2102), with an area (G, K) of (2143661–)2977888(–4052127) μm2 vs. (2602565–)2974201(–3352525) μm2 and (1385242–)1652749(–1865272) μm2 vs. (1496874–)1721106(–1842522) μm2. In the first subgroup, the width of single lobes (E1, E2) fell within a range of (1178–)1592(–1962) μm and (1250–)1568(–1779) μm and, in the second, was equal to (1435–)1516(–1700) μm and (1452–)1535(–1602) μm, with the width in the middle part of the stigma (F) in a range of (621–)915(–1237) μm vs. (950–)1018(–1128) μm. The length of upper and lower separation in the middle part between lobes (B, C) was (185–)257(–345) μm and (110–)309(–389) μm for P. arenaria and P. caesia, compared to (230–)247(–263) μm and (190–)224(–337) μm recorded in P. bohemica and P. purpurea. The angle between 2-lobed stigma in the upper and lower part (H, I) fell into a range of (106–)125(–140)° vs. (100–)122(–130)° and (103–)124(–156)° vs. (101–)108(–121)° (Table 2, Fig. 6).

The stigmas of species belonging to the sect. Phelipanche i.e. P. ramosa was oval to hemispherical with separated lobes which were white or bright bluish, rarely yellowish (Table 2, Figs 3U, 4H). The length of 2-lobed stigma (A, J) was the smallest of all Orobanchaceae stigmas tested, comprising (1159–)1544(–1700) μm and (1052–)1306(–1500) μm with an area (G, K) of (991449–)1524220(–1893740) μm2 and (365241–)468177(–589117) μm2. The width of single lobes (E1, E2) fell into a range of (811–)1115(–1274) μm and (814–)1072(–1274) μm, as well as the width in the middle part of the stigma (F) was equal to (413–)608(–766) μm. The length of upper and lower separation in the middle part between lobes (B, C) fell within a range of (163–)209(–264) μm and (200–)257(–317) μm and the angle between 2-lobed stigma in the upper and lower part (H, I) fell into a range of (78–)98(–116)° and (90–)110(–118)° (Table 2, Fig. 6).

Morphometric analysis

The analysis of data from the observation of stigmas structures identified twenty-one morphological characters of stigmas in Orobancheae (Table 2). UPGMA analysis based on characteristics suggested two types of stigma morphology, the first one included 2-lobed, occasionally 3- and 4-lobed stigmas which were oval, rarely hemispherical in shape and most often white, rarely light blue and yellowish with separated lobes. This cluster was represented by all Phelipanche species studied (Fig. 5). A separate subgroup consisted of P. ramosa stigmas characterised by being the smallest of all stigmas tested, as well as by their more hemispherical shaped stigmas in relation to other Phelipanche. The second type comprised the largest group of Orobanche species studied with 2-lobed, occasionally 3- and 4-lobed stigmas, mostly hemispherical to rounded or rarely oval and varied in colour from white, yellow, orange, pink, purple, red to dark brown with partially fused or separated lobes. This group was highly varied in terms of most useful identifying features, such as subtype, the length of 2-lobed stigma (A, J), the area of 2-lobed stigma (G, K), the width of single lobes (E1, E2), the width in the middle part of the stigma (F), the length of upper and lower separation in the middle part between lobes (B, C) and the angle between 2-lobed stigma in the upper and lower part (H, I). These features allowed several subgroups of stigmas to be distinguished corresponding to systematic and phylogenetic groups (Fig. 5). The first subgroup consisted of O. gracilis stigmas, which were the largest stigmas of all Orobanchaceae tested. Orobanche caryophyllacea, O. lutea and O. teucrii stigmas created a subgroup that stands out from the rest, with hemispherical to oval stigmas and two distinctly separated stigma lobes. O. alsatica and O. bartlingii stigmas reached one of the largest sizes after O. gracilis (Table 2, Fig. 6). The most diverse group on the UPGMA was represented by stigmas of the species from the Curvatae subsection, where three subgroups were distinguished (Fig. 5). The first of them, consisting of the stigmas of O. alsatica and O. bartlingii, was further away from the other representatives of this subsection due to quantitative features, for example, these stigmas were larger in relation to the other representatives such as: O. elatior, O. flava, O. kochii, O. lucorum and O. mayeri. The next subgroup, corresponding to O. coerulescens and O. cumana, had the smallest stigmas of the genus Orobanche that were analysed with a characteristic colour from white to yellowish-white, rarely bluish. Orobanche artemisiae-campestris, O. hederae, O. minor and O. picridis stigmas formed a separate subgroup of small stigmas (on average up to 2500 μm in length) with lobes in closer proximity or even partially united. A distinctive feature of the stigmas of this subgroup was also the presence of a well-developed and convex surface in relation to the base of the stigmas. The last subgroup, O. alba and O. reticulata, had stigmas which consist of a specific shape from spherical to rounded with two lobes in closer proximity and reaching similar sizes (Fig. 5).

Discussion

In order to provide diagnostic information and to evaluate the utility of stigma morphological characters considered in a taxonomic and phylogenetic context, a more thorough study on stigma morphology of representatives of Orobanchaceae was performed. For this purpose, we selected species representing various localities from Central Europe and applied stereomicroscopy to provide additional evidence for distinguishing genera, sections or subsections, as well as some related species of Orobancheae.

Orobanche and Phelipanche genera can be divided into two groups on the basis of the analysis of features carried out in this study. It was found that some quantitative features (e.g. the length of 2-lobed stigma (A, J), the area of 2-lobed stigma (G, K), the width of single lobes (E1, E2), the width in the middle part of the stigma (F), the length of upper and lower separation in the middle part between lobes (B, C), the angle between 2-lobed stigma in the upper and lower part (H, I) and the type and subtype of the stigma) are the best diagnostic characteristics for distinguishing these genera (Fig. 5). The stigmas in Phelipanche were the smallest of the species studied, usually not more than 2.5 mm in length of 2-lobed stigma (A) (Table 2, Fig. 6). There was a clear difference in the size of the stigmas between the analysed sections in Phelipanche. The stigmas of species belonging to the sect. Phelipanche i.e. P. ramosa were smaller (up to 1700 μm) than the species representing the sect. Trionychon (Arenariae) (the minimum length of 2-lobed stigma (A) was 1858 to 2089 μm) (Table 2, Fig. 6). Morphological, ecological and molecular differences suggest that P. bohemica have been a separate species (Piwowarczyk 2012, 2015; Piwowarczyk et al. 2015, 2018). Morphological studies of stigmas also showed differences between P. purpurea and P. bohemica, which had yellow-white stigmas in contrast to P. purpurea which was whitish (Table 2). Furthermore, the analysis of characteristics of stigmas confirmed the separation of two species of the problematic complex O. alsatica aggr. Orobanche alsatica and O. bartlingii were different in the shape and in the length of the mouth of the stylar canal (slit), which was more regular in O. alsatica, as well as there being a larger separation in the lower part between lobes in O. bartlingii (Figs 4A2, B2, 6). However, the similarity was evident in size, for example, both species were larger than the rest of the species in subsect. Curvatae. Orobanche coerulescens and O. cumana (sect. Inflatae) have been a transitional position between Orobanche and Phelipanche. They were placed on phylogenetic trees outside the rest of Orobanche (Piwowarczyk et al. 2018, 2021), which correlated with some phenotypic features (such as the violet colour of the flowers and white stigmas) or tricolpate pollen (in O. coerulescens) (Piwowarczyk et al. 2015) that made them similar to Phelipanche species. Our studies confirmed that the stigma characteristics corresponded to Orobanche. However, based only on the colour of the stigmas, they were close to Phelipanche (Fig. 5). Species belonging to the section Minores (incl. subsect. Hederae) (O. artemisiae-campestris, O. hederae, O. minor and O. picridis) and the section Inflatae (O. coerulescens and O. cumana) were clearly distinguished from others on the basis of their length of 2-lobed stigma (A) (µm), usually not more than 3 mm in Orobanche (Table 2, Fig. 6). O. hederae (which is surprisingly regarded as a member of the Inflatae section, following Teryokhin et al. 1993) was clustered on phylogenetic trees with species belonging to the subsect. Minores (Piwowarczyk et al. 2018) and our stigma morphology (Fig. 5) supports the supposition that these species are relatives.

In addition, phylogenetic studies support seed and pollen micromorphological analysis and it is noteworthy that this study showed the separation of the subgroups into separate species, based on the morphological analysis of stigmas which corresponded to systematic and phylogenetic groups (Piwowarczyk et al. 2018, 2021). Consequently, ITS dendrograms and cluster analysis (UPGMA) were similar, for example, showing a clear difference between the morphology of the stigmas of Orobanche and Phelipanche (Fig. 5). In conclusion, the often well-defined features of the stigmas had value both as taxonomic characters and as phylogenetic data for systematic studies. Additionally, the stigmas of the pistil of other members of the tribe Orobancheae, i.e. Cistanche and Phelypaea genera, have not been thoroughly investigated morphologically. However, there are some papers describing their shape and colour. Cistanche species are often subglobose in shape and usually white, yellowish or bluish, while stigmas in Phelypaea are usually discoid to subglobose with red, pink, rarely yellow colours (e.g. Teryokhin 1997; Piwowarczyk et al. 2019).

Morphological analysis of the stigmas of Central European broomrapes showed that they were characterised by high variability at the intergeneric and interspecific level. The morphology of the stigmas has consistently provided additional data to the other characters of flower morphology used to separate species, i.e. the type and subtype of stigma, the length of 2-lobed stigma (A, J), the area of 2-lobed stigma (G, K), the width of single lobes (E1, E2), the width in the middle part of the stigma (F), the length of upper and lower separation in the middle part between lobes (B, C) and the angle between 2-lobed stigma in the upper and lower part (H, I) (Table 2). Interestingly, the available publications of observations of the shape of stigmas in the Orobanchaceae concerned mainly the analysis of this feature in the front view. However, as our research showed, the most useful features can be seen when observing the stigmas from the bottom side, which has not been studied before. The features studied allow us to distinguish between species taking into account both dry, as well as FAA solution material. Additionally, the length of single lobes (A1, A2) and the area of single lobes (G1, G2) could be helpful when using larger samples. Features such as shape, colour and the degree of stigma lobes separation also have diagnostic value and allow us to distinguish species and genera in Orobanchaceae (e.g. Kreutz 1995; Piwowarczyk et al. 2019; Thorogood and Rumsey 2021), based on these characters. Moreover, the colour of the stigmas and petals of the same individual were often contrasting and differ from each other. Therefore, it is important to observe fresh material because the colours of the flowers of holoparasitic species in the field turn to different shades of brown after drying.

Although the taxonomy of some Orobanchaceae is still controversial, the morphology of stigmas could provide the next important characters used to define species. In this study, we used fresh plant material, dried and fixed in FAA solution. According Heslop-Harrison (1992), the most informative images or morphological analysis of stigmas are obtained using fresh, unfixed and uncoated material, because methods where the material is processed are unnecessary and leave some artefacts. Furthermore, it is extremely important that the morphological features of the mature stigmas are observed and collected at the stage when the stigmas are receptive for pollination. Additionally, the use of a stereoscopic microscope in research on the morphology of stigmas of Orobanchaceae are another possibility for differentiating taxonomically problematic species. Teryokhin et al. (1993) analysed the morphological differences of the stigmas of about 50 taxa of Orobanche and Phelipanche genera. In this paper, several types of stigmas were mentioned, i.e. discoid, discoid-bilobed, bilobed, two-columned-discoid, as well as two-columned stigma. This division proposed by Teryokhin et al. (1993) concerned the analysis only of the shape of the stigmas and the degree of separation of the lobes. Unfortunately, taking only these features into account, we cannot come to a conclusion about the usefulness of stigmas’ features for the taxonomy of Orobanchaceae (Teryokhin et al. 1993), except on a general level. Our observations showed that the degree of stigma separation of a particular species varies depending on the stage of stigma development and was difficult to observe and measure and, therefore, this feature should not be taken into account in separate systematic considerations. In conclusion, the paper of Teryokhin et al. (1993) is the only work known to us that draws wider attention to the morphology of the stigmas of holoparasites from Orobancheae. According to Yang et al. (2002), a study of stigma features and other parts of flowers when considered together can allow a better understanding of the process of floral evolution of hemiparasitic Pedicularis, especially their significance in pollination adaptation.

Heslop-Harrison and Shivanna (1977) classified Orobanche s.l. stigmas as dry stigmas with unicellular papillae, but sometimes the secretion may appear under a detached surface cuticle when it has been damaged by pollinating insects. Interestingly, the morphological adaptations of the stigmas were critical for optimum capture of pollen grains. According to Heslop-Harrison and Shivanna (1977), trinucleate pollen tends to be associated with dry stigmas. However, binucleate pollen occurs with both wet and dry stigmas and, in the case of Orobanche, the pollen is binucleate and the stigmas are dry. However, the basic subdivision in some families (e.g. Onagraceae) has been problematic and, in some cases, no clear separation can be made (Heslop-Harrison 1981). Amongst angiosperms families, Orobanchaceae is distinguished by the diversity in stigma type, in contrast to most families, in which stigmas are homogeneous (Heslop-Harrison 1981).

Conclusions

Comparative studies will be required to test further findings about the morphological determinants in stigmas of such variation in the Orobanchaceae family. The possibility of using the morphology of the stigmas may help explain taxonomic relationships in the identification of specimens of problematic taxa. Flowers, including stigmas of holoparasitic plants, have evolved several adaptations for pollination as a process of their parasitic strategies. In addition, floral characters have a special significance in the investigation of parasitic plants whose life cycle has led to a reduction of vegetative structures. A study of the floral stigmas may be useful to systematics and to obtaining knowledge of ecological and co-evolutionary adaptations between the parasites and their pollinators, as well as habitats. Stigma morphology is a highly informative taxonomic criterion that helps to resolve ambiguities in plant taxonomy and evolution and has proved to be a valuable complementary tool for Orobanchaceae species identification. It is noteworthy that this study supports the division between Orobanche and Phelipanche, as well as subgroups of stigma morphology corresponding to systematic and phylogenetic groups. Our research shows that the most useful features can be seen when observing the stigmas from the bottom side (previous research were related only to observations mainly from the front view), an aspect which has not been studied before. A comprehensive survey of the general and species of holoparasitic Orobanchaceae may lead to a better understanding of the floral morphology of the family.

Acknowledgements

We would like to thank Karol Zubek and Joanna Posłowska (Jan Kochanowski University) for stereomicroscope photographs.

This research was funded in part by National Science Centre, Poland [no. 2021/05/X/NZ8/01154]. For the purpose of Open Access, the author has applied a CC-BY public copyright licence to any Author Accepted Manuscript (AAM) version arising from this submission. This work was also supported by grants from the Jan Kochanowski University (no. SUPB.RN.21.244 and SUPB.RN.22.132).

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