The researchers stated that at early developmental stages the epidermal, endothecial
and middle layer cells had prominent nuclei, large vacuoles, numerous rough endoplasmic reticula and mitochondria.
The polarized endothecial
thickening of Mutisioideae is shared with Carduoideae and Cichorioideae, although in some tribes other types of thickening may exist (Bremer, 1994).
In anther sacs the endothecial
layer, comprising structurally weak fibrous cells, is the most common site of dehiscence.
Individual floral buds are susceptible to heat 9 to 7 d before anthesis, and the injury involves premature degeneration of the tapetal layer and lack of endothecial
development (Ahmed et al., 1992).
Additional characters listed by Kunze (1996) that support a position in the Asclepiadeae for Tylophora are: the lack of endothecial
tissue in the guide rails, and the degree of reduction of the endo thecium around the locules and in the structure of the guide rails.