Homalia pennatula (Musci: Neckeraceae), a New Combination from Southeast Asia, with a Key to the Species of Homalia

Abstract

Symphyodon pennatulus (Dixon) Dixon from Southeast Asia is transferred to the genus Homalia of the Neckeraceae (Musci). A key to the five species and one variety of Homalia is provided. Homalia (Bridel) Schimper is primarily distributed in the northern temperate regions and nearby subtropical borders, where it grows on boulders, rock outcrops, or bases of trees. It is characterized by strongly complanate plants with leaves arranged in distinct ranks; by oblong-ovate to spatulate leaves with broad apices and smooth leaf cells; and by smooth capsules with a hypnoid peristome. Symphyodon Montagne has 14 species worldwide and is primarily distributed in the tropical and subtropical regions of Southeast Asia, with one species in Hawaii, South Africa, and Central and South America, respectively. In Southeast Asia, it grows exclusively on tree trunks and tree branches. Besides its habitat distinction, taxonomic characters of generic importance for Symphyodon are found in the capsule ornamentation and peristomes. It has echinate capsules and an isobryoid peristome. Other secondary gametophyte features include: leaves often appressed and imbricate or spreading; leaf apices narrowed; and leaf cells prorate. Symphyodon pennatulus (Dixon) Dixon was excluded from the genus Symphyodon, because it is epilithic and has strongly complanate to sub-distichous leaves (He & Snider, 1992). The type specimen of Symphyodon pennatulus is meager and contains no sporophytes. Since no other specimens of this species were available, He & Snider (1992) were uncertain of its generic placement. Recently, numerous collections of this moss have come from Thailand, and though they consistently lack sporophytes, we now have enough material to make detailed observations on the gametophytes. Symphyodon pennatulus exhibits many aspects of Homalia, such as a strongly complanate habit, a homalioid-type leaf insertion showing an eight-ranked phyllotaxy (see He, 1992), oblong-ovate to spatulate leaves with broad and rounded apices, and a variable costal morphology. It is similar to the widely distributed Homalia trichomanoides (Bridel) Schimper in overall similarities of leaf shape and the absence of pseudoparaphyllia, but it differs in having distinct double costae and linear, projecting median leaf cells. On the basis of the double leaf costae and elongate median leaf cells, Symphyodon pennatulus appears most closely related to Homalia glabella (Hedwig) Schimper from Central and South America, except that it lacks pseudoparaphyllia. Although the narrowly linear and projecting median leaf cells of Symphyodon pennatulus and its presence in southern Asia differ from those of previously recognized Homalia species, the overall gametophyte features of this moss support its placement in Homalia. Hence, we are making the following new combination. A key to the five species and one variety of Homalia now recognized is provided. A description and an illustration of the species treated here will be published in the forthcoming revision of Homalia by the first author. Homalia pennatula (Dixon) He & Enroth, comb. nov. Basionym: Stereodon pennatulus Mitten ex Dixon, Rec. Bot. Surv. India 6: 66. 1914. Symphyodon pennatulus (Dixon) Dixon in Brotherus, Nat. Pflanzenfam., ed. 2, 11: 267. 1925. TYPE: Myanmar (Burma). Moulmein, Parish s.n. (holotype, NY; isotype, BM). In his book entitled Burma, Its People and Productions, Mason (1883) published a list of plants, including mosses. Homalia erosa Hampe and Homalia pennatula Mitten were listed in this publication. Both names are apparently nomina nuda, since no descriptions or basionyms were given. The former is clearly a herbarium name, because we have seen several herbarium specimens annotated with the name Homalia erosa Hampe. However, we have seen no specimens bearing the name Homalia pennatula Mitten, nor has it ever been published NovoN 5: 334-335. 1995. This content downloaded from 157.55.39.164 on Thu, 07 Jul 2016 06:15:41 UTC All use subject to http://about.jstor.org/terms Volume 5, Number 4 He & Enroth 335 1995 Homalia pennatula from Southeast Asia validly. Although it could be based on Mitten's herbarium name Stereodon pennatulus, Homalia pennatula Mitten has no nomenclatural bearing in our