Volume 7 NOVONNumber 41997Holomitrium hawkinsii (Musci: Dicranaceae), A New Species from Central America, and a Key to Holomitrium in Central America Bruce Allen Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166-0299, U.S.A.ABSTRACT. Holomitrium hawkinsii differs from allother species in the genus by its dioicous conditionwith full-sized male and female plants. It is closeto H. pulchellum, an entire-leaved species of Hol-omitrium, but is a larger plant with longer, moreslender leaves that have upper margins obscurelyand distantly dentate to spiculose, and lower leafmargins distantly serrulate. A key to the seven spe-cies of Holomitrium in Central America is given. In Central America the genus Holomitrium (Di-cranaceae) is usually found at relatively high ele-vations growing as an epiphyte on humus mats andthe roots of other vascular epiphytes in tree cano-pies. It also occurs on upper tree trunks and oc-casionally on humus over boulders. It is acrocar-pous and a member of the haplolepidous series ofmosses. On account of its short capsule neck, pa-pillose and irregularly divided (although sometimesentire) peristome teeth, narrow costa, phaneroporicstomata, well-developed alar cells, and differenti-ated perichaetial leaves the genus is placed in sub-family Dicranoideae of the Dicranaceae. Membersof Holomitrium are generally robust, have strong,narrow, single costae, distinctly different basal andupper leaf cells, well-developed alar cells, long-sheathing perichaetial leaves, cucullate calyptrae,erect capsules, subulate-rostrate opercula, and var-iously divided (sometimes undivided) peristometeeth. There are recent treatments of Holomitriumfor Mexico (Ireland, 1994) and the Caribbean (He-gewald, 1978). Allen (1990, 1994) treated six Cen-tral American species, one of which (H. pulchellumMitten) he considered so polymorphic that it mightrepresent two species. On the basis of recent fieldexperience, an evaluation of many new collections,and a re-evaluation of the original collections ofthis taxon, it now appears that H. pulchellum (astreated by Allen, 1990, 1994) represents two dis-tinct species, one of which is new to science.Holomitrium hawkinsii B. H. Allen, sp. nov. TYPE: Honduras. Lempira: Montana de Ce-laque, summit Cerro Mojon, 13 km SW of Gra-cias, 2849 m, 14�32'N, 88041'W, Allen 12240 (holotype, MO; isotypes, NY, TEFH, US). Fig-ure 1A-J. A H. pulchello Mitten statura grandi, foliis angustis,sexu dioico, marginibus superis foliorum obscure et dissitedentatis vel spiculatis, marginibus basilibus foliorum dis-site serrulatis differt. Plants large, tufted, greenish yellow to brownishyellow, corticolous or humicolous. Stems erect to 6cm high, branches few, irregular, simple. Leavescrowded, erect at base spreading above when wet,twisted to spirally contorted, crispate above whendry, variably undulate at margins, keeled. Leaveslanceolate from a narrowly ovate base, long, slen-derly acuminate, 5-8 mm long, margins erect tonarrowly recurved above, undulate, weakly and dis-tantly serrulate at base, dentate to spiculose at mid-dle, serrate at extreme apex, unistatose, costastrong, percurrent, upper and median leaf cellsrounded, quadrate, short rectangular or oblate, 8-10 �m long, 6-14 pm wide, incrassate, cell wallsstraight, basal leaf cells linear, 40-100 p�m long,6-8 pm wide, incrassate and pitted, alar cells poor-ly developed, fugacious, upper and basal leaf cells+ sharply demarcated. Dioicous. Male plants full-sized, perigonia terminal, with growth continued by NOVON 7: 329-332. 1997.