Cactoideae seeds show considerable variation in their shape, size, structure and testa color (Barthlott and Hunt, 2000).
The number of seeds per fruit may also depend on the age and size of the plant, the number of flowers produced, and the origin (wild or cultivated species), as demonstrated for Cactoideae (Parker, 1987; Leon de la Luz and Dominguez-Cadena, 1991; Rojas-Arechiga et al.
Further work on the mechanisms of germination is needed, particularly on the requirements for the germination of seeds of other Cactoideae, with the aim of contributing to their use, management and conservation.
Barthlott W, Hunt D (2000) Seed Diversity in the Subfamily Cactoideae.
Terrazas T, Arias S (2003) Comparative stem anatomy in the subfamily Cactoideae.
Berger (1929) recognized Schumann's subfamilies and the 41 genera in Cactoideae that were grouped in two tribes, Cereeae and Rhipsalideae.
Basic anatomical features of Cactoideae have been studied since the sixteenth century, focusing on selected features related to the different external forms or to stem photosynthesis.
He observed that leaves are vestigial in all of the Cactoideae species he studied.
Anatomical characters are rarely incorporated into phylogenetic analyses of Cactoideae.
For this analysis, 41 genera of Cactoideae were selected to represent the nine tribes proposed by Barthlott and Hunt (1993); two genera of Opuntioideae were also selected.
Dermal features appear to be the most informative stem characters in several groups of Cactoideae.