Seed ontogeny of Chamaecrista and its systematic implications in Cassiinae (Leguminosae, Caesalpinioideae)

The genus Chamaecrista originates from the dismembering of Cassia L., which was elevated to the level of subtribe Cassiinae, giving rise to Cassia sensu stricto, Chamaecrista, and Senna. Phylogenetic analysis has suggested that Cassiinae is not monophyletic. The relationships between its genera are not clear, because they sometimes appear close to Chamaecrista and Senna and at other times close to Senna and Cassia. We describe here development of the seeds of three species of Chamaecrista and compare our data with information published in the literature for Cassiinae and non-Cassiinae legumes. The ovules appear well conserved in Cassiinae, differing only in the length of the funiculus. In terms of seed development, the shape of the endosperm haustorium is similar in Senna and Chamaecrista. Chamaecrista shares more characteristics of its mature seeds with Senna than with Cassia. Chamaecrista and Senna have variable seed shapes, the presence of pleurograms, the absence of root cap primordia, a short epicotyl, and the cotyledonary mesophyll tends to be dorsiventral. These seed characteristics place Senna close to Chamaecrista and distance it from Cassia. We also observed characteristics unique to Chamaecrista, for example the occurrence of multiple pleurograms, a partially multiplicative seed coat, and the presence of embryonic colleters.