EARLY DEVELOPMENT OF ANDROECIA IN POLYSTEMONOUS HYDRANGEACEAE

Polystemonous androecia are diverse in both number and position of sta mens. This investigation of polystemonous Hydrangeaceae uses developme ntal data to characterize (1) the range of developmental variations th at account for the diverse androecial patterns and (2) how the express ions of polystemony among Hydrangeaceae compare to those found general ly among other angiosperms and especially in their sister family, the Loasaceae, some of which have particularly complex androecia. All poly stemonous Hydrangeaceae share the common element of stamen clusters in antesepalous positions. In each of these taxa, the first stamens are initiated opposite the medians of the sepals. Subsequently, stamens fo rm laterally on the flanks of the initial antesepalous stamens, giving rise to the clusters designated as antesepalous triplets. The simples t elaborations based on those common initial developmental steps inclu de (1) adding additional lateral flanking stamens and (2) adding a sin gle stamen in each antepetalous position between adjacent antesepalous groups. More complex elaborations are characteristic of (1) Carpenter ia and Philadelphus, which form common primordia at the beginning of a ndroecial development and, subsequently, have stamen primordia form on them, and (2) Deinanthe, which has an elongate hypanthial region on w hich numerous whorls of stamens are initiated. Carpenteria is unique a mong Hydrangeaceae in having groups of stamens that are initiated cent rifugally in antepetalous positions, and this is similar to complex el ements found among some Loasaceae. Generally, the polystemony of Hydra ngeaceae that is based in the formation of antesepalous triplets is ve ry similar to that found to evolve in parallel among various clades of rosids and asterids.