Research Article |
Corresponding author: Quentin Groom ( quentin.groom@plantentuinmeise.be ) Academic editor: Hugo de Boer
© 2021 Quentin Groom, Sofie Meeus, Steven B. Janssens, Leen Leus, Ivan Hoste.
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:
Groom Q, Meeus S, Janssens SB, Leus L, Hoste I (2021) Hybridization of Oxalis corniculata and O. dillenii in their non-native range. PhytoKeys 178: 17-30. https://doi.org/10.3897/phytokeys.178.61031
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Many species have been introduced beyond their native ranges and many have become global weeds. Human mediated dispersal has removed the geographic isolation of these species, reversing millions of years of independent evolution. Examples are the Oxalis species in section Corniculatae where several species have become invasive. Here we characterize and formally describe a hybrid between O. dillenii and O. corniculata, which occurs spontaneously in Belgium and Japan. Oxalis corniculata is probably native to Japan, but both species are alien to Belgium and O. dillenii is native to North America. We formally name this hybrid as Oxalis × vanaelstii. Although this hybrid is sterile, it is nevertheless vigorous and perennial. Both parent species grow as weeds in gardens; therefore, it is likely to be more common than currently appreciated in countries where these species co-occur.
DNA content, Oxalis × vanaelstii, pollen, stomata
The human mediated redistribution of plant species, whether by accident or design, facilitates the hybridization of species that were once separated by millennia of independent evolution (
The genus Oxalis is one of the weediest genera and many species have become naturalized beyond their native ranges (
Molecular genetic techniques have shown that hybridization has been an important force in the evolution of Oxalis (
Studies have indicated that hybridization can occur between species in the section Corniculatae (
For some years, one of the authors (IH) has maintained a small living collection of Oxalis species in his home garden in Aalter (Belgium, prov. of East Flanders). Among these plants are Oxalis corniculata var. atropurpurea and O. dillenii, both collected as weeds in plant containers offered for sale in garden centers and nurseries (although the former taxon was already present in the garden as a weed years before additional plants were deliberately introduced for cultivation). The precise origin of the cultivated plants is not known. Over the years, plants have escaped from the pots in which they are cultivated, as ripe seeds are catapulted away over distances that frequently exceed 1 m. It is among these escapees that, in 2016, putative hybrids were detected (voucher BR0000025668254V, see the taxonomic description). A few more plants of the possible hybrid were also found in 2017 and 2018. They grew next to plants of the two parents and flowered abundantly, yet produced no fruits. They were observed in a neglected part of the garden where selective manual weeding created opportunities for several different Oxalis to maintain themselves among competitors such as Epilobium sp., Poa annua and other common weeds. The hybrid grew on moderately damp, sandy, humus-rich soil. We note that all populations are homostylous.
Oxalis dillenii
Belgium. • Museumstraat 93, Bellem, Aalter; 51°05'44.46"N, 3°29'47.21"E; 8 Aug. 2013; Ivan Hoste 13023 (BR (BR0000013236892)).
Oxalis corniculata var. atropurpurea
Belgium. • Museumstraat 93, Bellem, Aalter; 51°05'44.46"N, 3°29'47.21"E; 2 Jul. 2019; Ivan Hoste (BR (BR0000025959222V)).
We applied a modified CTAB protocol for total genomic DNA isolation (
Genome sizes were measured with a Partec PAS III flow cytometer equipped with an 20 mW 488 nm solid state laser. Samples were prepared using the commercial kit Cystain PI absolute P (Partec, Germany). Each of the three plants of interest, O. corniculata, O. dillenii and the new hybrid were analyzed separately and chopped with a sharp razor blade at room temperature together with an internal standard (Zea mays, 2C = 5.43 pg,
Epidermal leaf impressions were made from the abaxial side of the leaves in the middle of the leaf, between the midvein and edge. Transparent nail polish (Bourjois Crystal ball) was used to make the impressions which, once dried, were mounted pointing upward with double-sided tape (Scotch) on a microscope slide.
Stacked photomicrographs were taken per leaf print (view fields = 0.09 mm2) using a digital microscope (VH-5000 Ver 1.5.1.1, Keyence Corporation) with full coaxial lighting and default factory settings for shutter speed at ×1000 lens magnification (VH-Z250R).
Anthers were collected from mature buds and no distinction was made between the two whorls of anthers. Material for scanning electron microscopy was washed in 70% ethanol for 20 minutes and washed twice with 100% DMM (dimethoxymethane) for 20 minutes while being sonicated each time for a couple of seconds. Then it was washed with 100% acetone. The material was critical point dried using liquid CO2 with a Leica EMCPD3000 critical point dryer. The dried samples were mounted on aluminum stubs using carbon adhesive tape and coated with a platinum palladium mix with a Cressington JFC-2300/208HR sputter coater. SEM images were obtained with a JEOL JSM7100F field emission scanning electron microscope. Pollen size was measured on 200 grains for each parent and for the hybrid. The diameter of the roughly spherical pollen was measured horizontally on the photograph regardless of orientation of the pollen grain. Pollen viability was measured using the staining protocol of
Oxalis corniculata var. atropurpurea has purple-brown leaves and O. dillenii bright green leaves (Figs
Guard cell length (µm), pollen diameter (µm) and total (2C) DNA content (pg) for O. corniculata, O. × vanaelstii and O. dillenii.
O. corniculata | O. × vanaelstii | O. dillenii | |
---|---|---|---|
Guard cell length (µm) | 23.9 (2.0, n = 45) | 18.0 (1.9, n = 119) | 18.4 (2.2, n = 39) |
Pollen diameter (µm) | 31.0 (3.1, n = 200) | 20.2 (6.2, n = 200) | 26.5 (2.6, n = 200) |
Total DNA content 2C (pg) | 2.13 (0.03, n = 5) | 1.50 (0.06, n = 8) | 0.88 (0.05, n = 7) |
The stipules and stem of the putative hybrid are illustrated in Figure
Stem and petiole hairs are also visible on Figure
Total DNA content (2C) is 0.88 pg (SD = 0.05, n = 7) for the O. dillenii parent, 2.13 pg (SD = 0.03, n = 5) for the O. corniculata parent and an intermediate DNA content of 1.50 pg (SD = 0.06, n = 8) for the putative hybrid.
Representative pollen grains of the parents and the hybrid are illustrated in Figure
ITS polymorphisms between O. corniculata and O. dillenii occurred at nucleotide positions 51, 52, 102, 103, 115, 122, 130, 138, 152, 165, 178, 187, 224, 232, 235, 237, 379, 423 (Fig.
Part of the aligned electropherogram of the nuclear ribosomal marker ITS for the hybrid taxon O. corniculata × dillenii and its putative parental accessions Oxalis corniculata (QG351) and O. dillenii (QG320). Double peaks and nucleotide ambiguity codes (R,Y,M,S) indicate that taxon QG321 has been the result of hybridization. Numbers above the sequences refer to nucleotide positions.
The DNA sequencing results are consistent with our sterile plant being a hybrid of O. corniculata and O. dillenii. The nuclear ITS sequence has ambiguity at each of the polymorphic loci between the proposed parent species, which suggests the hybrid genome contains alleles of both parents. The chloroplastic marker, trnL-F, differs in only one nucleotide in O. corniculata and O. dillenii. This single polymorphism indicates that O. dillenii is the likely maternal parent. This also accords with the results of
Our results agree with, and add to those of,
Holotype. Belgium. • Bellem, Aalter; 51.09°N, 3.49°E; 31 Oct. 2016; Ivan Hoste 16054 (holotype: BR (BR0000025668254V); isotype: K, isotype: MO).
Paratypes. Belgium. • Cultivated at Meise Botanic Garden; Quentin Groom 19001 (BR (BR0000025668247V)). • Cultivated at Meise Botanic Garden; Ivan Hoste & Quentin Groom S.N. (BR (BR0000025668209V)).
Intermediate in characters between its parents O. corniculata and O. dillenii. Prostrate to ascending, mid-sized stipules, stem hairs antrorse, not tightly appressed to the stem. Flowers with at most weak orange marks in the throat, marks sometimes absent.
A short-lived perennial, prostrate to ascending, herb with a thin taproot. Leaves trifoliolate with three similarly sized, heart-shaped leaflets. A narrow stipule is fused to the base of the petiole and is intermediate in width between O. corniculata and O. dillenii. The stem hair density is moderate with simple, arcuate, antrorse, pointed hairs. Not strongly appressed to the stem as in O. dillenii. The leaves are green or purple-brown, though if purple, not as darkly colored as Oxalis corniculata var. atropurpurea. The flowers are yellow, sometimes with weak orange streaks in the throat. Fruits are unknown.
Oxalis × vanaelstii is named to commemorate the Belgian naturalist, conservationist and mycologist Etienne Vanaelst (1948–2017) who, as a volunteer collaborating with mycologists at Ghent University, contributed to a better understanding of the diversity of mushrooms, especially those growing in and around his hometown, Knesselare (prov. of East Flanders).
Gardens.
Europe and Japan where parental distribution overlaps. The hybrid is also highly likely to occur in North America where the parents also co-occur (
The authors would like to thank Alison Northup and Kenneth Oberlander for their reviews, and Iris Van der Beeten for her help with the electron microscopy and pollen viability measurements. This work makes use of collections and data provided by Meise Botanic Garden as part of the Belgian contribution to the DiSSCo Research Infrastructure (FWO I001721N).
Figure S1
Data type: image
Explanation note: Part of the aligned electropherogram of the plastid gene marker trnL-F for the hybrid taxon O. corniculata × dillenii and its putative parental accessions Oxalis corniculata (QG351) and O. dillenii (QG320).
Taxonomic details of Oxalis × vanaelstii and its parents
Data type: COL
Explanation note: A Darwin Core file containing the details of Oxalis × vanaelstii, O. dillenii and O. corniculata.