Steyermarkochloa unifolia, A New Genus from Venezuela and Colombia (Poaceae: Arundinoideae: Steyermarkochloeae)

Abstract

Steyermarkochloa unifolia Davidse & Ellis, gen. et sp. nov. and Steyermarkochloeae Davidse & Ellis, trib. nov. are described. This species occurs in seasonally inundated white-sand soils in the Territorio Federal Amazonas, Venezuela, and Comisaria Guainia, Colombia. It has dimorphic culms and leaves. Only a single developed leaf is produced per vegetative culm. The morphology of this leaf is unique in the Poaceae in its cylindrical, solid sheath with flattened blade and absence of a ligule. Plants are polygamo-monoecious but most spikelets are unisexual. All spikelets are 3-flowered with the terminal floret always rudimentary. Male and bisexual spikelets usually have two fully developed florets, the lower usually male in bisexual spikelets, and are borne basally in the inflorescence. Female spikelets have the lower floret sterile and the second fertile. Lodicules are absent and the stamens and stigmas are terminally exserted. Anatomical studies indicate that the plant is arundinoid in all epidermal characteristics except the absence of microhairs and in most diagnostic characteristics of the blade anatomy. Steyermarkochloa is unusual in possessing vascular bundles inserted at different levels in the blade. The blades, sheaths, and roots have an extensive system of lacunae, a feature typical of aquatic plants. Although anatomical features clearly point to an arundinoid affinity, the many anomalous morphological features indicate an isolated position within the subfamily that is best recognized at the tribal level. During his intensive studies of the savannas in the Territorio Federal de Amazonas, Venezuela, Otto Huber collected an unusual grass along the Rio Temi in 1978 that could not be identified with any known Venezuelan species. A thorough search in the national herbarium ofthe Direccion de Investigaciones Biologicas (VEN) led to the discovery of an earlier unidentified collection of the same species made by E. Foldats in 1960 along the Rio Atabapo, also in Amazonas. In