Developmental and Structural Section
Richards, Jennifer , Baksh, Shanaz .
An architectural model of morphology for Eleocharis (Cyperaceae): Theme and variations.
THE aquatic sedge genus Eleocharis is unusual in having upright photosynthetic stems and non-photosynthetic leaves. Species can be cespitose, rhizomatous or stoloniferous. E. cellulosa has an iterative architectural model that is already established in seedlings. Photosynthetic culms are produced by sympodial growth of a vertical shoot; each module of the sympodium consists of three bracts with short internodes, an elongated photosynthetic internode beneath a fourth bract, and a terminal inflorescence that either aborts in vegetative culms or expands in reproductive culms. Renewal growth of the vertical shoot comes from a bud axillary to the first bract, while horizontal spread of the shoot system comes from a bud axillary to the second bract. The renewal bud reproduces the sympodial module. The second bract bud produces a horizontal shoot, initially by activity of a single apex, but growth becomes sympodial after 2-4 bracts are produced. Horizontal shoot sympodial modules have elongated first internodes, but are arrested distally. This horizontal shoot reorients and produces sympodia with short internodes, forming a new vertical shoot. Using dissections of field-collected material, we examined E. interstincta, E. elongata, and E. geniculata for presence of this architecture in order to understand how architectural variations lead to different growth forms. In these species vertical sympodial growth resembles that of E. cellulosa, and renewal and expansion buds are found in the axils of the first and second bracts, respectively, as in E. cellulosa. Horizontal shoot growth differs among the four species in orientation, in amount of internodal elongation, and in developmental potential of the distal portions of the sympodial modules. These data suggest that the sympodial model is fundamental to the architecture of the genus, while variation in growth form is achieved through variation in outgrowth of buds axillary to the second bract, i.e., in development of the horizontal shoot.
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1 - Florida International University, Deparment of Biological Sciences, 11200 SW 8th St., Miami, Florida, 33199, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 303/Bell Memorial Union
Date: Wednesday, August 2nd, 2006
Time: 9:15 AM