Plant Ecology and Evolution 146(3): 310-327, doi: 10.5091/plecevo.2013.844
Development of reproductive organs in Canephora madagascariensis (Octotropideae - Rubiaceae)
expand article infoPetra De Block, Alexander Vrijdaghs
‡ Meise Botanic Garden, Nieuwelaan 38, BE-1860 Meise, Belgium
Open Access
Background and aims – Ontogenetic studies provide valuable morphological characters to aid interpretation of evolutionary scenarios. But they are rare within the Rubiaceae and the variation in floral ontogenetic patterns in the different Rubiaceae lineages remains underexplored. Here, we provide the first developmental study of the reproductive organs of Canephora madagascariensis, a typical representative of the poorly known tribe Octotropideae in most of its characters except for its unique, flattened, assimilating, 'phylloclade-like' inflorescences. Methods – Using SEM and LM we produced a developmental study of inflorescence, flower and fruit in C. madagascariensis . Key results – The inflorescence of Canephora madagascariensis is a condensed dichasium. Peduncle, first-order bracts and first-order branches together form a flattened, green, phylloclade-like structure, showing both leaf and stem characters. Initially, the dome-shaped floral apex becomes concave and sepals are formed. Next, from the collar of the concave apex, a tubular corolla with epipetalous stamens grows out. Meanwhile, an inferior bilocular ovary is formed. Per locule, up to seven unitegmic ovules are formed on a U-shaped placenta. Fruits are drupes with one to several fibrous seeds with folded exotesta. Conclusions – The double-organ identity of the green, flattened part of the inflorescence is due to a modification leading to leaf analogy. The peculiar inflorescence of C. madagascariensis constitutes just another state of the character 'axillary inflorescence' in Rubiaceae. It results from both reduction and congestion, two trends typical in Rubiaceae inflorescences. Floral cups form the basis of the floral structure in Canephora . The inferior ovary is due to the initial formation of a hypanthium, from which calyx lobes, stamen-corolla tube, corolla tube sensu stricto and calyx tube originate through successive outgrowth of underlaying annular intercalary meristems.