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 <em>Digitaria filiformis </em>complex, to determine the proper taxonomic rank and rarity of each taxon. The taxonomy of the <em>D. filiformis </em>complex is highly debated and includes two widespread species, <em>D. filiformis </em>and <em>D. villosa</em>; a possibly extinct species endemic to a single-site in New Hampshire, <em>D. laeviglumis</em>; and a rare species of southern Florida and the West Indies, <em>D.</em><em> dolichophylla. </em>We conducted morphologic comparisons and molecular analysis of the four members of the <em>D. filiformis</em> complex, together with specimens from Mexico and Venezuela purportedly identified as <em>D. laeviglumis</em> (morphology only). Based on results of phylogenetic analyses of plastid and nuclear ITS sequences and morphologic comparisons, we recognize five species in the <em>D. filiformis </em>complex, including a newly described Mexican endemic <em>D. glabrifloris. </em>After field investigation we have moved the global rank of <em>D. laeviglumis </em>from globally historical (GH) to extinct (GX), as there is virtually no likelihood of rediscovery. <em>Digitaria</em><em> dolichophylla </em>is much rarer than previously recognized, moving from secure (T5) to imperiled with extinction (G2).本研究针对细穗马唐（Digitaria filiformis）类群开展系统研究，旨在明确各分类单元的合理分类等级与濒危程度。细穗马唐类群的分类学界定长期存在较大争议，原类群包含4个类群：2个广布物种——细穗马唐（D. filiformis）与绒毛马唐（D. villosa）；1个可能已灭绝的狭域特有物种，仅分布于美国新罕布什尔州的单一分布点，即光稃马唐（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种长叶马唐（D. dolichophylla）。本研究对细穗马唐类群的4个成员，以及墨西哥与委内瑞拉境内仅基于形态学特征被鉴定为疑似光稃马唐的标本开展了形态学比较与分子分析。基于质体与核内转录间隔区（ITS）序列的系统发育分析结果，结合形态学比较，本研究认定细穗马唐类群共包含5个物种，其中包括新描述的墨西哥特有种光花马唐（D. glabrifloris）。经野外调查后，本研究将光稃马唐的全球濒危等级由“历史存在（GH）”调整为“灭绝（GX）”，因目前几乎不存在重新发现该物种的可能性。长叶马唐（D. dolichophylla）的稀有程度远超此前认知，其濒危等级已从“安全（T5）”调整为“濒危（G2）”。