Based on morphological and molecular evidence (DNA sequences from six plastid regions: atpβ, rbcL, trnG-trnR, trnL-trnF, atpβ-rbcL, and rps4-trnS), the new fern species Leucotrichum madagascariense is described from Madagascar, where it is found in the North (Marojejy), Centre (Andringitra), and South (Andohahela) regions. Leucotrichum madagascariense has long, whitish laminar hairs, among the other distinguishing characters of the genus: arching fronds, laminar apices subconform to the lateral pinnae, dark sclerenchyma covered by the green laminar tissue, and laterally marginate petioles. Its most remarkable feature is the lack of rhizome scales, a character that is shared with the Neotropical L. pseudomitchelliae. However, our phylogenetic results suggest that this character has evolved twice independently within the genus. In contrast, the sister relationship between the new Madagascan species and the group composed of L. schenckii and L. mortonii is morphologically supported by linear and deeply pinnatifid laminae, incised 2/3–3/4 of the way to the rachis along its length. Leucotrichum madagascariense is the only representative of the genus known from the Old World. Because it is nested within a clade of five Neotropical species, we hypothesize that its occurrence outside the Neotropics results from one long-distance dispersal event from America, likely southeastern Brazil, to Madagascar.
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Vol. 37 • No. 2