Floral ontogeny and morphology of Cevallia, Fuertesia, and Gronovia (Loasaceae Subfamily Gronovioideae)

Abstract

Members of Loasaceae subfamily Gronovioideae have distinctive flowers compared to those of other members of the family. In contrast to all other Loasaceae, they have haplostemonous androecia and uniovulate gynoecia. The haplostemonous androecia are paedomorphic. The two major clades of gronovioids—(1) Petalonyx and (2) Cevallia, Fuertesia, and Gronovia—differ in their avenues of diversification. The clade consisting of Cevallia, Fuertesia, and Gronovia has floral variation that is manifested most prominently in stamen, stigma, and nectary forms, although petal shapes and the positions of anthers relative to petals and stigmas also vary. The Petalonyx clade exhibits variation that is manifested in morphological differentiation among stamens (Petalonyx crenatus has staminodes) and in postgenital fusion in the corolla (lacking only in Petalonyx linearis and P. crenatus). Developmental studies have also shown that Gronovioideae share with their sister group Mentzelia the loss of a petal‐stamen synorganization that is present in other investigated members of Loasaceae.