Early floral development and androecium organization in the sarracenioid clade (Actinidiaceae, Roridulaceae and Sarraceniaceae) of Ericales

The early floral development of Actinidia ( A. arguta , A. callosa , A. chinensis and A. kolomikta ; Actinidiaceae), Saurauia ( S. montana , S. oldhamii , S. pittieri and S. subspinosa ; Actinidiaceae), Roridula gorgonias (Roridulaceae) and Heliamphora nutans (Sarraceniaceae) was studied comparatively using scanning electron microscopy. Late stages of androecium development are additionally presented for Clematoclethra scandens (Actinidiaceae), Darlingtonia californica and Sarracenia leucophylla (Sarraceniaceae). Flowers are typically pentamerous and share a number of developmental features: perianth organs emerge in a clockwise or anticlockwise spiral sequence on the floral apex with relatively long plastochrons between successive organs, resulting in conspicuous size differences among perianth organs in early development; the perianth always consists of two differentiated whorls (unlike earlier interpretations of the perianth in Heliamphora ); the androecium is polystemonous in most species and is initiated with leading stamens in alternipetalous positions; successive stamen primordia appear in a lateral succession until a ring‐like structure is formed; and the anthers become inverted shortly before anthesis. Later androecial development differs conspicuously between taxa and further proliferation may be centrifugal, centripetal and/or lateral. For Ericales, unusual features of floral development include: petals initiated in a spiral sequence (but later organized in a whorl) with comparatively long plastochrons between individual petals (except Saurauia ); common occurrence of perianth organs in double positions in Actinidiaceae; and anthers that become inverted close to anthesis. The floral development in the sarracenioids is additionally compared with that of other families and clades in Ericales, further emphasizing the highly variable patterns of androecium development in the order.