Leaf and scape anatomy of Leiothrix Ruhland (Eriocaulaceae) from a taxonomic and ecological perspective

Abstract

Leiothrix is endemic to South America with 47 species, only two of which do not occur in Brazil. Its distinguishing characters are habit, dialypetalous or gamopetalous corolla of the male flowers and presence or not of pseudovivipary. According to Ruhland's monograph (1903) there are five subgenera. Recent molecular and morphological analyses of the family show the genus to be monophyletic, but infrageneric relationships are not well established. The study objective was to investigate leaf and scape anatomy of representatives of the four subgenera that occur in Brazil in order to contribute to the taxonomy and better understand the plants' environmental adaptations. Leiothrix anatomy is similar to that of other Eriocaulaceae genera: leaves and scapes have a single-layered epidermis, collateral vascular bundles are surrounded by a double sheath, leaves have stomata only on the abaxial side, and scapes have alternating vascular bundles of larger and smaller size. Leiothrix subg. Rheocaulon is monospecific, leaves have a single vascular bundle, scapes lack ribs, the epidermal cells have slightly thickened walls, and the cortex contains collenchyma and chlorophyllous parenchyma. In L. subg. Eleutherandra the leaf epidermis cell walls have homogeneous thickening at the margins, specialized substomatal chambers, a hypodermis, and sclerenchymatous extensions of the vascular bundle sheaths. Most taxa of L. subg. Calycocephalus have smaller vascular bundle sheath extensions facing both surfaces and ribbed scapes. Species from Minas Gerais have a hypodermis and up to seven leaf vascular bundles; those from Bahia lack a hypodermis and have more than seven leaf vascular bundles. L. subg. Stephanophyllum has scapes with a cylindric multilayered pericycle with thickened and lignified cell walls. These anatomical structures partly corroborate the subgenera proposed by Ruhland, suggest the existence of other infrageneric groups and reflect the environmental adaptations of the studied species.