onsdag 29 januari 2014

Nomenclature and systematics

The genus Eranthis has its nomenclatural history in Linnaeus’ Species Plantarum from 1753. Linnaeus treats it as Helleborus hyemalis together with Helleborus niger, H. viridis, H. foetidus and H. trifolius (now Coptis trifolia (L.) Salisb.). In 1807 the winter aconites got their own genus when Salisbury published his essay on the genera of Trollius, Eranthis, Helleborus, Coptis and Isopyrum. In his introduction Salisbury describes the doubt which should push the taxonomic science centuries on:

“Our first vernal flower, the Winter Aconite, which I lately saw in great abundance, has given rise to the above reflections. This plant appears to me a distinct genus, nor can I find any affinity whatever in it, to that in which it has hitherto been placed, beyond the common characters of the order; for the same Nectaria occurs in several others.” (Salisbury 1807)

Over two centuries have past and still we treat the common winter aconite as a good species in a distinct genus. Several new species was described in the 1900-century as a result of exploration of East Asia. The new taxa described by Maximowicz, Turczaninow, Franchet and Candolle hade white flowers and other distinct characters as round tubers and stalked flowers. Maybe Nakai was hit by the same thought as Salisbury when he 1937 published a new generic name for the Asiatic species. He included E. keiskei (now E. pinnatifida Maxim.), E. albiflora, E. longistipitata, E. sibirica, E. stellata and E. uncinata (now E. sibirica) in the new genus Shibateranthis. Nakai distinguished these species by the round tubers, stalked flowers and the elongated stigma. Left for Eranthis (senso stricto) was E. hyemalis and E. cilicica. (Nakai 1937)

Nakai’s treatment was never widely accepted but the name was kept by Tamura in 1987 when he changed its status to sectional level. For Tamura Eranthis was Eranthis but dividable to the sections of Shibateranthis and Eranthis. In the former E. sibirica, E. uncinata, E. stellata, E. albiflora, E. lobulata and E. pinnatifida was placed whereas E. hyemalis (with E. cilicica included) and E. longistipitata was placed in section Eranthis. (Tamura 1987) In 1995 Tamura explains this statement in the key to the sections: Eranthis form a new tuber yearly to make a rhizome and the upper margin of the petals is emarginated or bilobate without swellings. Shibateranthis do not form a rhizome by yearly growth but a tuber and the petals are bilobate or biforked and have lobes with swellings.

The latest contribution to the debate was Luferov’s treatment of Shibateranthis at subgenus level in 2004. He suggests E. pinnatifida, and its synonym E. keiskei , E. lobulata, E. stellata, E. longistipitata, E. albiflora, E. sibirica and the synonym E. isurica (= E. cilicica) for subgenus Shibateranthis and E. hyemalis and E. cilicica for subgenus Eranthis. Luferov follows mostly the treatment of Nakai and explains his statement by spherical tubers, stalked flowers, white, pale yellow or pinkish sepals and elongated stigma for subgenus Shibateranthis.

For such a small genus as Eranthis with only nine species it seems to me premature to talk about subgenus or to divide it into several genera. There is not yet any extensive DNA proofing beside the morphological characteristics, so while waiting for future investigations it seems most arguable to keep the sectional level. However, the main two treatments of Nakai and Tamura are both problematic. Tamura do not agree with Nakai when he puts E. longistipitata to section Eranthis because of the shape of petals and the rhizomatous tuber. Tamura also keep E. albiflora in section Shibateranthis despite its emarginated petals which lacks swellings. By this position he acts against his own sectional key in Tamura 1995.

A phylogenetic investigation confirms a sectional dividing of the genus Eranthis as Tamura 1987 suggests. Based on ten morphological characteristics the nine species was analysed and the two sections was confirmed. The phylogenetic web of figure A links all species with four or less differing characteristics; consequently the most related species. The number by each link indicates the numbers of differing characteristics. As the illustration shows only E. longistipitata bridges E. hyemalis and E. cilicica with the rest of the genus. 

When the web reduces by removing all links of four characteristics a clear dividing of the genus appears, the three yellow flowering species of section Eranthis divide from the white flowering of section Shibateranthis (figure B). 

In next step (figure C) all links of three characteristics are removed. The two groups of E. pinnatifida/byunsanensis and E. sibirica/stellata/lobulata appears but also the outlying position of E. albiflora. The latter is linked to six other species and making it the most linked taxon but only by weak links of four and three characteristics. 

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