Floral Ontogeny and Histogenesis in Leguminosae.

Abstract

Inflorescence organogeny and floral initiation are investigated topographically (using scanning electron microscopy) and histogenetically in Acacia baileyana (Mimosoideae) and Lupinus havardii (Papilionoideae). Floral ontogeny is investigated topographically in Parkinsonia aculeata (Caesalpinioideae). The paniculate racemes of A. baileyana are constructed of first- and second-order inflorescence meristems. Each produces first-order and second-order bracts, respectively, in acropetal order. Each of the former bracts subtends one second-order inflorescence meristem while the latter bract type subtends a single flower. The radially symmetrical floral meristem of A. baileyana produces calyx members in helical order and corolla members simultaneously with a precocious terminal carpel. Common stamen primordia are initiated in antisepalous sites. Three to five individual stamen primordia form on each of the common stamen primordia after which additional stamen primordia appear laterally to fill in antipetalous areas between the common stamen primordia. Proliferation of the androecium is accomplished after radial expansion of the floral apex providing space upon which individual stamen primordia may encroach upon the expanded apex to the base of the carpel. Terminal racemes of L. havardii. pa produce bracts in acropetal order. Each bract subtends one flower. The bilaterally symmetrical floral meristem of L. havardii produces all floral organs in a unidirectional sequence within each whorl with some members of each whorl appearing precociously to the rest. Flowers of P. aculeata are initiated on racemes in acropetal order and each flower is subtended by a bract. The floral meristem of P. aculeata produces sepals in helical order and the other floral organs in unidirectional order. Precocious appearances of the carpel is consistent in all three species investigated. Its terminality is documented histologically only the papilionoid and the mimosoid taxa.