What kind of seed dormancy occurs in the legume genus Cassia?

Abstract

Cassia is a diverse legume genus widespread in the (sub-)tropical zone of the world. Several studies have been done on this genus; however, significant changes have occurred at the taxonomic level over the years. this has led to inaccurate information about seed dormancy in Cassia since many species are no longer included in the genus. thus, our work aims to investigate and update the information about the kind of dormancy that occurs in seeds of Cassia species and also look into two notorious species in this group (C. fistula and C. javanica) to compare myxospermous vs. non-myxospermous seeds regarding dormancy and germination traits. Seed dormancy reports were found for 53 Cassia species, and the only kind of seed dormancy found for these species was physical dormancy (pY). nondormancy was not found, and all seeds had a blockage to water uptake during the dormant state, that is, all have PY. Of these 53 species, only 18 are currently included in the genus Cassia. C. fistula and C. javanica have fully developed embryos, and dormancy is only conferred by the (water-impermeable) seed coat. the lens in the seed coat is the only structure that creates a water pathway to break pY in C. fistula. Myxospermous seeds came out of dormancy faster than non-myxospermous ones. PY seems to be the only kind of seed dormancy that has evolved in Cassia. The extent of this kind of dormancy in all subtribe cassiinae is also discussed. Cassia L. sensu stricto was first proposed by Irwin and Barneby 1,2 , who segregated Cassia sensu lato into three genera (Cassia L., Chamaecrista Moech. and Senna Mill.), establishing the subtribe Cassiinae (Leguminosae: Caesalpinioideae). The genus Cassia was considered as the largest genus in Caesalpinioideae 3,4 , but currently it is comprised of only about 30 species 5. Their fruits usually are indehiscent (also divided by transversal septa), unlike those of Senna, which are typically dehiscent and without septa separating the seeds 2. The woody indehiscent pods of Cassia are quite tough, as well as the seeds. Additionally, Cassia fruits are not fleshy, but with remnants of pulp. The presence of these fruit traits suggests that large mammals could disperse Cassia seeds. However, a possible absence of seed dispersers for some species leads to speculation that these indehiscent fruits were likely dispersed by megafauna that are now extinct. Janzen and Martin 6 reported that some fruit traits are better related to extinct animals (seed dispersal anachronisms), since some tough fruits may not be consumed (and seeds dispersed) by smaller extant animals. The absence of dispersers affects seed fate 6 , not only because of the lack of dispersal but also due to the ability of dispersers to break over the tough fruits and release the seeds. Concerning seed dormancy, Baskin and Baskin 7 proposed a classification system that includes five classes (see Baskin and Baskin 7), wherein dormancy is associated with the embryo or other seed components (e.g. the seed coat). Among these five classes of dormancy, physic...

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