Molecular and Taxonomic Reevaluation of the Digitaria filiformis Complex (Poaceae) including a Globally Extinct, Single Site Endemic from New Hampshire, USA, and a New Species from Mexico

We examine the Digitaria filiformis complex, to determine the proper taxonomic rank and rarity of each taxon. The taxonomy of the D. filiformis complex is highly debated and includes two widespread species, D. filiformis and D. villosa; a possibly extinct species endemic to a single-site in New Hampshire, D. laeviglumis; and a rare species of southern Florida and the West Indies, D. dolichophylla. We conducted morphologic comparisons and molecular analysis of the four members of the D. filiformis complex, together with specimens from Mexico and Venezuela purportedly identified as D. laeviglumis (morphology only). Based on results of phylogenetic analyses of plastid and nuclear ITS sequences and morphologic comparisons, we recognize five species in the D. filiformis complex, including a newly described Mexican endemic D. glabrifloris. After field investigation we have moved the global rank of D. laeviglumis from globally historical (GH) to extinct (GX), as there is virtually no likelihood of rediscovery. Digitaria dolichophylla is much rarer than previously recognized, moving from secure (T5) to imperiled with extinction (G2).

本研究针对线形叶马唐复合群（Digitaria filiformis complex）展开探究，旨在明确各分类群的合理分类等级与稀有程度。该复合群的分类学争议极大，此前的分类体系将其划分为4个类群：2个广布物种——线形马唐（D. filiformis）与绒毛马唐（D. villosa）；1个可能已灭绝的特有物种——仅分布于美国新罕布什尔州单一分布点的光稃马唐（D. laeviglumis）；以及1个分布于佛罗里达州南部与西印度群岛的稀有物种长叶马唐（D. dolichophylla）。本研究对该复合群的4个成员开展了形态学比较与分子分析，并纳入了据称被鉴定为光稃马唐的墨西哥及委内瑞拉标本（仅开展形态学研究）。基于质体（plastid）序列与核ITS（nuclear ITS）序列的系统发育分析结果，结合形态学比较数据，本研究确认线形叶马唐复合群内共包含5个物种，其中包括1个新描述的墨西哥特有物种无毛花马唐（D. glabrifloris）。经野外实地调查后，我们将光稃马唐的全球保护等级从全球历史存续（Globally Historic, GH）调整为灭绝（Extinct, GX），因目前几乎不存在重新发现该物种的可能性。长叶马唐的稀有程度远高于此前认知，其全球保护等级已从安全等级（T5）调整为极危濒临灭绝（G2）。