02733nas a2200157   4500008004100000245017900041210006900220300001200289490000800301520204500309653010502354100002402459700002102483700002102504856005002525       2005                        eng d00aEvolutionary transitions among flowers of perianthless Piperales: inferences from inflorescence and flower development in the anomalous species Peperomia fraseri (Piperaceae)0 aEvolutionary transitions among flowers of perianthless Piperales  a925-9430 v1663 aFloral and inflorescence structure and ontogeny are described in detail in Peperomia fraseri, an anomalous species of Piperaceae that differs in several respects from other species of Peperomia and other perianthless Piperales (Piperaceae and Saururaceae). Inflorescence structure is atypical in this species, with numerous spikes arranged spirally on a long raceme. There is a gender distribution of flowers along each spike, with the proximal (lower) part bearing bisexual flowers and the distal (upper) region bearing female flowers. Furthermore, there is a high degree of polymorphism in the structure (including presence or absence) of flower-subtending bracts in the same inflorescence. Bract suppression at the basalmost abaxial position in P. fraseri could be explained by a strong inhibitory activity of the spike-subtending bract or its primordium. Bract suppression among scattered flowers in the lower (bisexual) region is interpreted as an example of somatic instability. By contrast, more distal bract and stamen suppression seems to be part of a general tendency to flower reduction toward the spike apex in P. fraseri, where spatial constraints in the inflorescence control the size and shape of the bract and floral primordia, resulting in stamen suppression in smaller primordia. However, it is difficult to understand why an abracteate flower is formed in P. fraseri rather than a sterile bract, as in Peperomia hispidula. Furthermore, in contrast with most other Piperaceae, P. fraseri has no apical residuum on mature spikes; at least some partial inflorescences bear a terminal flowerlike structure, although this more closely resembles those of some Saururaceae than the "true" terminal flower of perianth-bearing Piperales, such as Aristolochiaceae. Peperomia fraseri and other atypical members of Piperaceae represent potentially useful models for examination of patterns of bract and stamen loss in perianthless Piperales, in which spatial constraints in the developing spike are important for floral construction.10abasal angiosperms, bract, floral evolution, ontogeny, Piperales, stamen suppression, terminal flower1 aRemizowa, Margarita1 aRudall, Paula, J1 aSokoloff, Dmitry  uhttps://juncaginaceae.myspecies.info/node/300