ANATOMY AND ASPECTS OF DEVELOPMENT OF THE STAMINATE INFLORESCENCES AND FLORETS OF SEVEN SPECIES OF ALLOCASUARINA (CASUARINACEAE)

The morphology, ontogeny, and vascular anatomy of the staminate inflorescences and florets of seven species of Allocasuarina are described. The generally terminal but open-ended inflorescences occur on monoecious or staminate dioecious trees and consist of whorls of bracts, each subtending a sessile axillary floret. Each floret consists of one terminal stamen with a bilobed, tetrasporangiate anther enclosed typically by cuculliform appendages, commonly considered bracteoles, an inner median pair and an outer lateral pair. The mature stamen is exerted, the anther is basifixed and is extrorsely dehiscent. In early development of a male inflorescence very little internodal elongation occurs and enclosing cataphylls appear. The inflorescence apex is a low dome with a uniseriate tunica and a small group of central corpus cells. Bract primordia are initiated by periclinal divisions of C₁ followed by further divisions of the corpus and anticlinal divisions in the tunica. The bracts are epinastic and become gamophyllous except apically by cell divisions in both sides of each primordium. Stomata are restricted to the axis furrows and the abaxial tips of the bracts. The axillary florets arise in acropetal succession initiated by periclinal divisions in C₁ accompanied by anticlinal divisions in the tunica. The lateral floral appendages are also initiated by C₁ followed by anticlinal divisions in the tunica. They become adnate basally later with the subtending bract. The median sterile appendages are initiated in a manner similar to the initiation of the outer appendages. The stamen is initiated by divisions in the outer layers of the corpus and in the tunica, and then develops first by apical growth followed by intercalary growth. The vascular system of the inflorescence is identical to that of the vegetative stem. Each floret is supplied by a single bundle that has its source in a branch from each of the two traces supplying a bract. Six bundles arise from the floral bundle; four of these terminate in the base of the stamen and two form an amphicribal bundle that supplies the anther. Pollen is binucleate, 3- to 7-porate. The exine is tegillate.