Date of Award

2003

Document Type

Thesis

Degree Name

Master of Arts

Department

Biology

Abstract

Acalypha deamii (Euphorbiaceae), once thought restricted to flood plains of the Ohio and mid-Mississippi River systems, is now documented from similar habitats in Virginia, Maryland, and West Virginia along the James, Potomac, Rappahannock, Roanoke (Staunton), and Shenandoah rivers. This species is recognized by two-carpellate gynoecia, large seeds, and the routine occurrence of allomorphic flowers and fruits, features sporadically found within this large genus. In addition to documenting the newly recognized range extension of Acalypha deamii, this thesis also investigates the nature of its allomorphic reproductive structures. Staminate, pistillate, fruiting, and allomorphic reproductive structures of Acalypha deamii and a closely related species, Acalypha rhomboidea, were studied using LM and SEM. Staminate flowers are composed of four crystal-encrusted valvate sepals and eight stamens that bear divergent vermiform anthers with helically thickened endothecium, amoeboid tapetum, and tricolpate pollen. Pistillate flowers are bracteate, but otherwise naked, two-carpellate (Acalypha deamii) or three-carpellate (Acalypha rhomboidea), and have bitegmic, crassinucellate, anatropous ovules arising from an apical, axile placenta. Fruits from pistillate flowers are covered with trichomes, some gland-tipped, some simple and uniseriate. Internally, fruit walls bear a prominent inner-zone of sclerifled cells involved in dehiscence and ballistic dispersal of seeds. Seeds are mottled tan to dark brown. Testa contains two prominent cell layers of the inner integument: the arcuate outer-most cells are sclerifled and the inner-most cells are tracheid-like. Internal anatomy of allomorphic reproductive structures largely matches those of typical pistillate flowers and fruits. In contrast with pistillate flowers, allomorphic structures lack gland-tipped trichomes but have a markedly muricate surface, a one-carpellate ovary that develops in a reflexed orientation, and more weakly developed mechanical layers in the fruit wall. Further, allomorphic seeds of Acalypha deamii possess weak sclerification within the testa. Notably, materials studied clearly show presence of embryos within allomorphic seeds of Acalypha deamii and Acalypha rhomboidea, evidence that these structures are fertile and viable.

Download

Included in

Biology Commons

Share

COinS