Systematic studies in 'Gomidesia' O. Berg (Myrtaceae)

Abstract

Gomidesia is a neotropical genus with a distribution centred on the Atlantic rain forest biome of southeastern Brazil. Most species of Gomidesia are confined to Brazil but a single species extends to the Antilles and another is known only from Bolivia and Argentina. Forty species are delimited and described in the present study. For each species, notes are provided on distribution, ecology, nomenclature and typification. A century of nomenclatural malpractice has resulted in much confusion in the application of names. In some cases conservation action is required to preserve existing usage of long-established binomials. The genus is distinguished from other genera of the Myrciinae by virtue of its relatively long anthers in which the thecal arcs retain some degree of curvature after dehiscence and the ventral pollen sacs are vertically displaced on the connective relative to the dorsal pollen sacs. Unlike the situation in other genera of the Myrciinae, in Gomidesia stamen number is not correlated with disk size. These features of the androecium may represent an adaptive response to buzz-pollination. Other characters observed in some species of Gomidesia and unknown elsewhere in the Myrtoideae include a sterile connective stub which separates the pollen sacs from the filament and a pubescent hypocotyl. Species of Gomidesia tend to flower later than other sympatric Myrtaceae and the fruit maturation period may extend over six months or more. Field observations indicate that pre-dawn anthesis and buzz-pollination are prevalent but not ubiquitous in Gomidesia and that populations of a single species may vary considerably in pollination ecology. Breeding system studies demonstrate that most species of Gomidesia are outcrossers but that there is no evidence of pre-zygotic discrimination against flowers hand-pollinated with self pollen. Preferential outcrossing in Gomidesia is maintained by a post- zygotic mechanism, the precise functioning of which remains to be elucidated.