Abstract
ABSTRACT Species of Apocynaceae stand out among angiosperms in having very complex flowers, especially those of asclepiads, which belong to the most derived subfamily (Asclepiadoideae). These flowers are known to represent the highest degree of floral synorganization of the eudicots, and are comparable only to orchids. This morphological complexity may also be understood by observing their glands. Asclepiads have several protective and nuptial secretory structures. Their highly specific and specialized pollination systems are associated with the great diversity of glands found in their flowers. This review gathers data regarding all types of floral glands described for asclepiads and adds three new types (glandular trichome, secretory idioblast and obturator), for a total of 13 types of glands. Some of the species reported here may have dozens of glands of up to 11 types on a single flower, corresponding to the largest diversity of glands recorded to date for a single structure.
Highlights
Apocynaceae is an extremely diverse family in morphological terms, represented by trees, shrubs, herbs and climbers, with single leaves usually opposite, rarely alternate or whorled, with stipules modified in colleters in several species (Endress & Bruyns 2000; Capelli et al 2017) and with various secretory structures in vegetative and reproductive organs of recognized importance in taxonomy, phylogeny and/or ecology (Thomas & Dave 1991; Demarco 2008)
Brown (1810) divided it into two families and this separation had been maintained in the subsequent taxonomic studies until recently (Cronquist 1981), many researchers have found a gradation in the morphology of the complex reproductive organs between the two families
Colleters are widespread in Apocynaceae (Endress & Bruyns 2000) and occur in flowers of all Asclepiadoideae
Summary
Apocynaceae is an extremely diverse family in morphological terms, represented by trees, shrubs, herbs and climbers, with single leaves usually opposite, rarely alternate or whorled, with stipules modified in colleters in several species (Endress & Bruyns 2000; Capelli et al 2017) and with various secretory structures in vegetative and reproductive organs of recognized importance in taxonomy, phylogeny and/or ecology (Thomas & Dave 1991; Demarco 2008). Due to their highly elaborate flowers, the family stands out among the eudicotyledons, especially when considering its most derived subfamily Asclepiadoideae. Phylogenetic studies carried out mainly during the 1990s have shown that the two families form a monophyletic group, constituting a single family
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