A Systematic Study of the Genus Lasiacis (Gramineae: Paniceae)

Abstract

A systematic treatment of the tropical South American grass genus Lasiacis is presented. The gross morphology of Lasiacis is discussed. Lasiacis is panicoid in the form of its leaves, its roots and its seedlings. Leaf anatomy was studied from cross sections of blades and from the epidermis. Lasiacis has a typically non-Kranz (C3) panicoid anatomy. It possesses the following major anatomical characteristics: 3 types of vascular bundles, angular secondary vascular bundles, partially radiate chlorenchyma around the vascular bundles, differentiated palisade and spongy chlorenchyma, double bundle sheaths around the primary vascular bundles, single parenchyma sheaths around the primary vascular bundles, single parenchyma sheaths around the secondary vascular bundles, short cells of costal zones in long rows, dumbbell and nodular Si bodies, bicellular microhairs and triangular to dome-shaped subsidiary cells. The breeding system is predominantly inbreeding with a smaller amount of outbreeding. All species tested are self-compatible. New chromosome counts of n = 18 and 2n = 36 are reported for 101 collections representing 13 spp. and 8 varieties. Reported for the first time are: L. anomala, L. divaricata var. divaricata, L. harrisii, L. linearis, L. oaxacensis var. oaxacensis and var. maxoni, L. procerrima, L. ruscifolia var. velutina, L. sloanei, L. sorghoidea var. sorghoidea and var. patentiflora and L. standleyi. Meiosis was completely regular. In the taxonomic treatment, 23 taxa [L. anomala, L. divaricata var. divaricata, L. divaricata, var. austroamericana, L. harrisii, L. ligulata, L. linearis, L. nigra, L. oaxacensis var. oaxacensis, L. oaxacensis var. maxonii, L. procerrima, L. rhizophora, L. ruscifolia var. ruscifolia, L. ruscifolia var. velutina, L. sloanei, L. sorghoidea var. sorghoidea, L. sorghoidea var. patentiflora, L. grisebachii var. grisebachii, L. grisebachii var. lindelieana, L. standleyi, L. scabrior, L. divaricata var. leptostachya, L. rugelii var. pohlii and L. rugelii var. rugelii] are recognized including 16 spp. and 13 varieties. A key to the species is provided. Synonymy, descriptions, discussions, distribution, ecology, common names, economic uses and herbarium specimens are given for each species.