Developmental morphology of Apinagia multibranchiata (Podostemaceae) from the Venezuelan Guyanas

Apinagia (c. 50 spp.) is the largest genus of American Podostemaceae. Apinagia multibranchiata (Matth.) Royen is a haptophyte endemic to the Venezuelan Guyanas. It fits well with the Podostemoideae bauplan known from other New World genera, such as Marathrum and Mourera. Shoots arise in pairs from filamentous creeping adhesive roots. During the rainy season submerged vegetative shoots grow up to more than a metre long. They are normally unbranched and provided wih distichously arranged leaves which are laterally flattened into one plane. The lanceolate leaves may show a fimbriate tip. Tufts of threads are found on the upper leaf surface which faces the sky. When the water recedes in December–January, ascending reproductive shoots (up to 15 cm long) are formed which branch sympodially. The first module produces a variable number of leaves. Distal leaves are often double-sheathed (dithecous). Their inner sheaths are fused into a tube that covers the first flower bud. Daughter modules arise from the outer sheaths of the distal leaves. These modules consisting of two double-sheathed leaves and a flower are repeated giving rise to 2–15 stalked flowers. The flowers are entomophilous and provided with 6–29 pink stamens. Architecture and developmental morphology of A. multibranchiata are compared with other members of the genus.