Reasons and consequences of the lack of a sporopollenin ektexine in Aroideae (Araceae)

Pollen morphology and pollination ecology of Amorphophallus species from North Western Ghats and Konkan region of India

“…Further, Tarasevich (1992) considered that susceptibility to acetolysis is a feature of most Araceae pollen. It is likely that the susceptibility of exine to the traditional acetolysis may be linked to the lack of a sporopollenin ektexine in Aroideae (Araceae) as suggested by Hesse (2006). However, our observations agree with those of Grayum (1992) that the pollen of the studied Amorphophallus species is not susceptible to acetolysis and retained an intact patterned surface.…”

Relationships within the Araceae: Comparison of morphological patterns with molecular phylogenies

“…This clade also includes most genera with spinose pollen exine (char. 12‐2; see also remarks by Hesse, 2006c), and while various patterns are present, spinose exine is otherwise typical only in the Lemnoideae. Although the clade is notable for the occurrence of osmophoric spadix appendices (Vogel, 1963), these are absent in 14 of the 37 genera and also occur elsewhere in several genera of Schismatoglottideae (clade 15, Aridarum, Bakoa, Bucephalandra, Schismatoglottis, Phymatarum ) and in a few species of Homalomena and Philodendron .…”

“…The remaining 75 genera form Aroideae (clade 39), which is well supported on both molecular and, when Calla is excluded (for discussion, see below), on phenotypic evidence by the following morpho‐anatomical synapomorphies: loss of the perigon, presence of laticifers, and loss of sporopollenin in the ektexine. Hesse (2006b, 2006c) has argued that taken together, these changes in morpho‐anatomical character patterns seem to imply a major adaptive shift in the evolution of aroids. In this clade, the omniaperturate pollen grains have a thick, spongy endexine and a highly reduced ektexine with either a very thin sporopollenin lamella or a nonsporopollenin outer exine layer (Hesse, 2006b).…”

“…But there is reason to remain skeptical of the position of Calla, at least pending further confirmatory evidence. The topology jars with the distinct phenotype of the unisexual‐flowered aperigoniate Araceae, whose evolution appears to be a key event in aroid phylogeny (Hesse 2006a, 2006b, 2006c). This is clearly a problem of great interest.…”

“…Particularly important fields of study involve leaf venation, seed structure, and pollen structure. While the latter two areas have been the foci of important studies in recent years (e.g., Grayum, 1992; Seubert, 1993; Hesse et al, 2001; Hesse, 2002, 2006a, 2006b, c; Tillich, 2003), comparative leaf venation of the Araceae has generally been neglected since the monograph by Ertl (1932).…”