Research Article |
Corresponding author: Rosa Cerros-Tlatilpa ( tlatilpa@uaem.mx ) Academic editor: Marcos A. Caraballo-Ortiz
© 2023 Maria Guadalupe Maldonado-Borja, Rosa Cerros-Tlatilpa, Luis Gil Galván-González.
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:
Maldonado-Borja MG, Cerros-Tlatilpa R, Galván-González LG (2023) A new species of Struthanthus Mart. (Loranthaceae) from Oaxaca, Mexico. PhytoKeys 225: 69-81. https://doi.org/10.3897/phytokeys.225.101238
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Struthanthus ibe-dzi sp. nov. is a new species described and illustrated from the cloud and pine-oak forests of the Sierra Madre del Sur in Oaxaca, Mexico. This species shares similarities of leaf shape and inflorescence type with S. deppeanus, S. quercicola, and S. ramiro-cruzii. However, S. ibe-dzi can be recognized by its glaucous branches, leaves and inflorescences; compressed nodes; convoluted distal half of styles in pistillate flowers; and staminate flowers with asymmetrical thecae and an extended connective forming an apiculate horn in both anther series. A distribution map and an identification key are provided to separate S. ibe-dzi from morphologically similar congeners present in the region.
Struthanthus ibe-dzi sp. nov., es una nueva especie descrita e ilustrada de los bosques de niebla y de pino-encino de la Sierra Madre del Sur en Oaxaca (México). La nueva especie se puede confundir con S. deppeanus, S. quercicola, y S. ramiro-cruzii por la forma de la hoja y el tipo de inflorescencia. Sin embargo, S. ibe-dzi se distingue por sus ramas, hojas e inflorescencias glaucas; sus nodos comprimidos; flores pistiladas con el estilo convoluto desde la mitad hacia la parte distal; y flores estaminadas con tecas asimétricas y un conectivo extendido apiculado en forma de cuerno en la serie baja de las anteras. Se incluye un mapa de distribución y una clave de identificación para separar S. ibe-dzi de sus congéneres regionales morfológicamente similares.
Endemic, hemiparasitic, mistletoes, taxonomy
Struthanthus Mart. is a neotropical genus in the Loranthaceae family with approximately 60–70 species (
Despite the lack of a comprehensive taxonomic treatment for Struthanthus, new species have been described during the last 20 years (
Regarding generic affinities, Struthanthus has been found to be closely related to Cladocolea. This relationship has been supported by pollen morphology as described in
About 14 species of Struthanthus have been reported from Mexico (
While preparing a floristic checklist for Struthanthus in Mexico, herbarium material and specimens collected during fieldwork were examined. The description provided below is based on our collections from Sierra Madre del Sur in the state of Oaxaca as well as herbarium specimens from ANSM, CHAPA, CIIDIR, ENCB, HUAA, HUAP, HUMO, IEB, MEXU, RSA, SLPM, UAMIZ, UAS, UAT, USON, XAL, and ZEA (acronyms follow Thiers (2021, continuously updated)).
Specimens were collected, pressed, and dried, with three to five duplicates per number. Vouchers were deposited at HUAP, HUMO, MEXU, and UAMIZ. All specimens gathered had reproductive structures (flowers and fruits) present. Morphological characters were measured from dried specimens and described using the terminology presented by
Mexico. Oaxaca: Tlaxiaco, Río Ocotepec, en el arroyo Yute kuini (San Juan del Río Cuquila), carretera Tlaxiaco-Putla, 17°10'26.48"N, 97°46'17.29"W [17.174022°N, -97.771469°W], 1962 m a.s.l., 30 Mar 2021, M.G. Maldonado, L.G. Galván G. & R. Cerros T. 21 (♀ fl, fr) (holotype: HUMO-39855!, isotypes: MEXU!, UAMIZ!).
Struthanthus ibe-dzi morphologically resembles S. deppeanus and S. quercicola in having epicortical roots on stems, similar leaf shapes, and inflorescences in racemes. However, the new taxon differs by its compressed nodes, stems, leaves, and inflorescence glaucous; leaf blade with base cuneate to oblique; staminate flowers 6–9 mm long with asymmetrical thecae and an extended horn-shaped apiculate connective in both anther series; and pistillate flowers with distally convoluted styles.
Aerial hemiparasitic woody shrub, pendulous, perennial, with epicortical roots present at the base of main trunk; branches pendant. Stems green when young, brown with lenticels when mature; nodes glaucous, bicarinate and compressed, especially when young; internodes terete, with epicortical roots. Leaves opposite or subopposite; petioles 0.25–1.2 cm long, twisted, forming a shallow channel from the raised edge of leaf blade; blades ovate to lanceolate, rarely elliptical, 5.0–12.2 × 1.4–5.0 cm, papyraceous when dried; apex acute to acuminate, base cuneate to oblique, margin entire to repand, hyaline, venation pinnate. Inflorescences a solitary raceme of triads, indeterminate and axillar; bracts and bracteoles caducous at or after anthesis, cymbiform; rachis subterete to compressed, nodes compressed, triads opposite or subopposite, decussate, green, glabrous, glaucous. Staminate inflorescence 2.0–6.8 cm long, peduncle 0.2–0.8 cm with 6–16 (19) triads, triad peduncle 0.10–0.58 cm long. Pistillate inflorescence 2.0–5.0 cm long, peduncle 0.2–1.0 cm long with 6–12 (15) triads, triad peduncle 0.18–0.86 cm long. Staminate flowers hexamerous, rarely pentamerous, flower buds clavate with rounded apex; central flower of triad sessile, lateral pedicels 0.28–1.3 mm long; mature flowers 6.0–9.0 × 2.0–2.3 mm, petals linear, reflexed near the apex, 4.4–7.9 × 0.8–1.2 mm, anthers basifixed (not versatile) in two series, theca asymmetrical; prominent connectival apiculate horn in both the lower and upper series; calyculus irregularly dentate, whitish, vestigial ovary 1.5–2.2 mm; pistiloid straight to sigmoid 1/3 near the apex, 2.8–6.5 mm long, stigma undifferenced; nectary thick with six protuberances surrounding the pistiloid base. Pistillate flowers hexamerous, flower buds cylindrical, rounded at the apex; central flower of the triad sessile, pedicels of lateral flowers 0.18–0.8 cm long, slightly accrescent when bearing fruit; mature flowers 5.8–7.2 × 1.6–2.2 mm, linear petals 5.2–5.6 × 0.8–1.0 mm, staminodes in one series; calyculus whitish, irregularly dentate, inferior ovary 1.7–2.0 mm; style convolute 4.0–5.2 mm long (± 3 longitudinal folds) from the middle to the apex, stigma capitate; nectary thick with six protuberances surrounding the style. Fruit a one-seeded berry, ovoid, 3.85–6.0 × 6.52–8.60 mm. Seeds ovoid, 3.0–4.7 × 5.1–7.4 mm. Figs
Struthanthus ibe-dzi (Loranthaceae) A base of stem and disk of secondary haustoria (sh) B epicortical root (er) and swollen stem of host plant by the penetration of secondary haustoria (sh) C staminate inflorescences with caducous bracts (bra) and bracteoles (brc) D dissected petals of staminate flower showing two series of stamens (S1, S2), with anthers in the lower series (S1) displaying a prominent connectival horn (cn); receptacle showing an undifferentiated pistilloid and a nectary (ne) surrounded by the calyculus E pistillate inflorescences and compressed node (arrow) F dissected pistillate flower showing vestigial staminodes (st) opposite to petals, and an inferior ovary with convoluted style and calyculus (ca) G upper view of ovary in a pistillate flower showing its calyculus (ca) and nectary (ne) H immature fruits crowned by the calyculus.
(Paratypes). Mexico. Oaxaca: San Juan Mixtepec, Yucu Shúun (Monte de Tesoro) a 16 km S de San Juan Mixtepec, 17°13'37.46"N, 97°47'54.5"W [17.22707°N, -97.78484°W], 2,500 m a.s.l., 8 Nov 1988 (♀ fr), J. Reyes S. 1064 (MEXU, UC/JEPS); Putla Villa de Guerrero, 2.1 km después de Santo Domingo Chicahuaxtla, hacia Putla, [17.142761°N, -97.848589°W], 2,050 m a.s.l., 5 Feb 1993 (♀ fr), M. Cházaro B. 7088 (CHAPA, ENCB, MEXU, XAL); Santiago Juxtlahuaca, El Manzanal, senda para la parcela del Sr. Hemeterio, entrada por Santa Rosa-San Miguel Cuevas, Distrito Juxtlahuaca, 17°13'13.20"N, 98°3'38.30"W [17.22033°N, -98.06063°W], 2,060 m a.s.l., 13 Sep 1996 (♀ fl, fr), J.I. Calzada 21381 (MEXU); San Juan Mixtepec, Camino a Santos Reyes Tepejillo, 1 km antes de la desviación al Capulín y Tinuama de Zaragoza, 17°19'23.4"N, 97°54'13.2"W [17.32317°N, -97.90367°W], 2,650 m a.s.l., 9 Apr 2019 (♂ fl), L.G. Galván G. & R. Cerros T. 474 (HUMO); Putla Villa de Guerrero, orilla de la carretera, km 92, 2.8 km antes de San Andres Chicahuaxtla, 17°10'48.20"N, 97°49'32.48"W [17.18014°N, -97.82569°W], 2,363 m a.s.l., 13 Feb 2020 (♀ fr), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 13 (HUMO); ibid, 13 Feb 2020 (♀ fr), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 14 (HUMO); Tlaxiaco, Río Ocotepec, en el arroyo Yute kuini (San Juan del Río Cuquila), carretera Tlaxiaco-Putla, 17°10'26.48"N, 97°46'17.29"W [17.17402°N, -97.77146°W], 1,962 m a.s.l., 30 Apr. 2021 (♂ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 19 (HUMO); ibid, 30 Apr 2021(♀ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 20 (HUMO); ibid, 30 Apr 2021 (♀ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 22 (HUMO); ibid, 30 Apr 2021(♀ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 23 (HUMO); Putla Villa de Guerrero, km 92, carretera Tlaxiaco-Putla, 200 m antes de La Cañada Tejocote, 17°10'48.38"N, 97°46'31.94"W [17.18010°N, -97.82554°W], 2,374 m a.s.l., 30 Apr 2021(♂ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 24 (HUMO); ibid, 30 Apr 2021(♀ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 25 (HUMO); ibid, 30 Apr 2021(♂ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 26 (HUMO); Putla Villa de Guerrero, Orilla de carretera de Tlaxiaco-Putla, en San Andres Chicahuaxtla, 17°09'42.16"N, 97°50'11.85"W [17.16171°N, -97.83662°W], 2,473 m a.s.l., 30 Apr 2021(♂ fl), M.G. Maldonado, R. Cerros T. & L.G. Galván G. 27 (HUMO).
Struthanthus ibe-dzi is endemic to Oaxaca, Mexico, where it is only known from cloud and oak-pine forests with secondary vegetation in the Sierra Madre del Sur (
Flowering from March to April and in September; fruiting in February to April and September to November. Individuals can be found bearing flowers and fruits on different branches.
The epithet ibe-dzi refers to the common name given to any mistletoe in Zapotec language (Ibë-dzí) in the San Juan Mixtepec region, which means “hair(s) on top of”, where “ibé” denotes “hair(s)” and “dzi” indicates “on top of”.
Struthanthus ibe-dzi is only known from the western part of the state of Oaxaca, near the border with the state of Guerrero (Fig.
Being a hemiparasitic plant with a complete dependence on hosts, mistletoe populations are vulnerable to the indirect effects of logging important host trees such as oaks (Quercus spp.), and habitat modification and fragmentation for livestock and agriculture (
Herbarium specimens of S. ibe-dzi have been previously identified as S. deppeanus, S. quercicola, or Struthanthus sp. However, the new taxon differs from S. deppeanus and S. quercicola by its compressed or bicarinate nodes and by having glaucous stems, leaves, and inflorescences which are covered by a whitish wax (observed in both fresh and dried specimens). In addition, S. ibe-dzi has one inflorescence raceme per axil, with peduncled triads with a sessile central flower and pedicellate lateral ones. The bracts and bracteoles are caducous, forming visible scars. Staminate flowers have asymmetrical thecae and an apiculate connectival horn in both series, while pistillate flowers have a convolute style with ± 3 longitudinal folds (Fig.
Struthanthus ibe-dzi, as other mistletoes in the San Juan Mixtepec region of Oaxaca, are locally known as birdlime vine, and known for the sticky substance (i.e., viscin) produced in the fruits, which is used to catch birds (
1 | All floral triads pedicellate; pedicels accrescent when bearing fruit | S. deppeanus |
– | Lateral floral triads pedicellate or subpedicellate, central one sessile; pedicels not accrescent when bearing fruit | 2 |
2 | Bracts and bracteoles persistent, mainly in pistillate flowers; style straight to sigmoid in pistillate flowers | S. quercicola |
– | Bracts and bracteoles caducous in both staminate and pistillate flowers; style convoluted to strongly convolute in pistillate flowers | 3 |
3 | Leaf base subcordate to truncate; staminate flowers 6–7 mm long; pistillate flowers 5.0–5.8 mm long | S. ramiro-cruzii |
– | Leaf base cuneate to oblique; staminate flowers 6–9 mm long; pistillate flowers 5.8–7.2 mm long | S. ibe-dzi |
Among the currently accepted genera of Loranthaceae, Struthanthus is one of the most taxonomically challenging since no monographic treatment exists (
Struthanthus ibe-dzi morphologically resembles S. deppeanus, S. quercicola, and S. ramiro-cruzii. All these four species have epicortical roots on stems and inflorescences in racemes. Struthanthus deppeanus, S. ibe-dzi, and S. quercicola have similar leaf shape ranging from ovate to lanceolate with a long acute apex (Table
Comparison of morphological characters among four species of Struthanthus (Loranthaceae) from Mexico: S. deppeanus, S. ibe-dzi, S. quercicola, and S. ramiro-cruzii.
Character | S. ibe-dzi | S. deppeanus | S. quercicola | S. ramiro-cruzii |
---|---|---|---|---|
Stem nodes | compressed and bicarinate | terete | terete | terete |
Leaf shape | ovate to lanceolate, rare elliptical | lanceolate to ovate-lanceolate | lanceolate to elliptic-lanceolate | ovate to lanceolate, cordate when mature |
Leaf apex shape | acute to acuminate | acute to long acuminate | attenuate to acuminate | apiculate or acute |
Leaf base shape | cuneate to oblique | acute | obtuse to round | subcordate to truncate |
Petiole length (mm) | 2.5–12 | 5–10 | 3–8 | 5–10 |
Inflorescences per axil | 1 | 1–2 | 1–2 | 1 (2) |
Triads per staminate inflorescence | 6–16 (19) | 8–10 | 8–16 | 10–12 |
Triads per pistillate inflorescence | 6–12 (15) | 8–10 | 6–12 | 8–14 |
Bracteoles persistence | caducous | caducous | persistent | caducous |
Pistillate flower length from base of ovary (mm) | 5.8–7.2 | 6.2–7.5 | 4.0–5.2 | 5.0–5.8 |
Style | convolute | sigmoid to slightly convoluted below the stigma | straight to sigmoid | strongly convolute |
Staminate flower length from base of ovary (mm) | 6–9 | 7.0–8.5 | 5.5–7 | 6–7 |
We are grateful to C.S. Caires, E. Martínez-Ambriz, and M.A. Caraballo-Ortiz for their comments and suggestions, especially to the latter for his valuable help to improve the manuscript. This work is part of the M.S. thesis of the first author and is financially supported by the National Council of Science and Technology (CONACYT) through grant 286670. We thank the curators from the herbaria cited in the Materials and Methods section for allowing access to their collections, particularly to IEB, MEXU, and XAL for processing specimen loans. We are also grateful to the Secretaría de Medio Ambiente y Recursos Naturales for granting a collecting permit (SGPA/DGGFS/712/1132/1809/N1-0081/04/18), and to the people from Río Ocotepec, Tlaxiaco, Oaxaca for providing facilities to collect plants specimens.
All authors contributed to the preparation of the manuscript by providing data and reviewing and editing the text. MGMB, LGGG, and RCT conducted the fieldwork, RCT provided photos of living plants, and MGMB prepared stereoscopic photographs and the taxonomic key. MGMB and RCT made the descriptions (measurements and morphological data) of the new species.