A Remarkable New Species of Acromastigum (Hepaticae) with Septate Rhizoids and Filamentous Gemmae

Abstract

Acromastigum gemmiferum is described as a new species from Sabah (North Borneo). The species is best characterized by septate rhizoids which are sometimes repeatedly forked, and filamentous gemmae composed of numerous, uniseriate cells. These characters are unique not only in the genus Acromastigum but also in the Hepaticae at large. Acromastigum (Lepidoziaceae), a well-defined genus characterized by the distinc- tive terminal branching (Acromastigum-type), comprises about 40 known species which are predominantly distributed in the Indomalayan-Australasian region. All taxa bear unlobed or bilobed, transverse to incubous leaves, except for the isolated species A. stenophyllum, which bears (2-)3-lobed, somewhat succubously oriented leaves; this is referred to the monotypic subgenus Triandrophyllopsis (Schuster, 1968). The most primitive members of the genus (sect. Acromastigum) are restricted to New Zealand and New Caledonia (with one species in Hawaii), while the more advanced members (sects. Subcomplicata, Exilia, and Inaequilatera) are radiated from there to Oceania, Indomalaya and, with a few species, disjunctively extended to South America (3 species in Patagonian region) and Africa (a single species in the southern extremes). The genus is most abundantly represented in Indomalaya, especially in Borneo, where 15 species have been known (Evans, 1934; Herzog, 1950; Grolle, 1964). As we have found several other species in rather small collections from Borneo, it is assumed that more species than hitherto recorded actually occur in Borneo. It is apparent, even judging from known taxa, that the genus has a chief center of speciation in Borneo and there exhibits great diversity and endemism, with many species deviating far from the type species, A. integrifolium. Acromastigum gemmiferum, a Bornean new species here proposed, seems to represent the culmination of one such deviation-being distinct from other known taxa of the genus in such outstanding features as septate rhizoids and filamentous gemmae. These have been known neither in Acromastigum nor in other genera of Hepaticae (except in the few cases noted below).