Comparative vegetative anatomy of Stanhopeinae (Orchidaceae)

Stanhopeinae are a group of tropical American orchids characterized by eugl ossine bee pollination and lateral inflorescences stemming from the bases o f pseudobulbs. Leaves are hypostomatal, and all stomatal configurations are tetracytic. Chlorenchyma is homogeneous and characterized by fibre bundles in adaxial/abaxial or adaxial/median/abaxial positions. Collateral vascula r bundles occur in a single row and feature phloic and xylic sclerenchymato us caps and thin-walled bundle sheath cells. Fibre bundles and vascular scl erenchyma are accompanied by stegmata containing conical silica bodies. Pse udobulbs have thick-walled turbinate epidermal cells and ground tissue of s maller, living assimilatory cells and larger, dead water-storage cells. Fib re bundles are usually absent but occur in several genera. Collateral vascu lar bundles show phloic sclerenchyma, but xylic sclerenchyma occurs only in the larger vascular bundles. Phloic and xylic sclerenchyma are associated with stegmata containing conical silica bodies. Roots are velamentous. Vela men cell walls have fine, spiral thickenings. Exodermal cells are thin-wall ed. The cortex features scattered thick-walled cells and in some cases bran ched bars of secondary cell wall material. Endodermis is either boolean OR- or O-thickened, but pericycle is always O-thickened opposite the phloem. V ascular tissue consists of alternating strands of xylem and phloem surround ed by a matrix of thick-walled cells. Pith cells may be parenchymatous or s clerenchymatous. (C) 1999 The Linnean Society of London.