Floral anatomy of Asian Schefflera (Araliaceae, Apiales): Comparing variation of flower groundplan and vascular patterns

Floral morphology and vascular anatomy in members of the Asian Schefflera clade (Araliaceae) are studied. This clade is of special interest because of secondary loss of flower groundplan stability and increase of merism. Among five species studied, three have isomerous pentamerous flowers, one has (almost) isomerous polymerous flowers, and one has nonisomerous flowers as a result of increased carpel number. Loss of calyx innervation and reduction of sepals are suggested as apomorphic for the subclade Heptapleurum s.l. Tupidanthus calyptratus, a member of this subclade with the most polymerous gynoecium among asterids, shares those features, too. Range of petal venation diversity within the species examined exceeds what was previously estimated for the family Araliaceae and the order Apiales. Formation of anastomoses between the bundles of petals and stamens in bisexual flowers of Schefflera venulosa is suggested as an effect of high auxin production in developing anthers. A shift of the ovule supply from ventral bundles to lateral ones occurs in different lineages of Apiales. Fusion between peripheral and dorsal bundles is an effect of flower topography that may not be considered an advanced character state. Strong differences in floral vasculature between closely related species with the same flower groundplan are highlighted.