Biology Reference
In-Depth Information
soon after [16]. The work of Grayum [17] that is re-examined here, provides hy-
potheses about the ancestral and derived states of pollen wall sculpturing within
the Araceae (monocots). His proposition that the most primitive aroid pollen had
foveolate to reticulate exine is not in contradiction with our phylogenetic analysis
of the character. Indeed, our results suggested that the hypothetical aroid pol-
len was either 'Foveolate/Reticulate' or 'Psilate' for pollen ornamentation (Figure
1A). The equivocal ancestral state is probably due to the polytomies, coded as soft
(uncertainty in resolution), that are present in the tree. From this equivocal type,
different types of sculpturing evolved [17]. However, no type of ornamentation
is restricted to one clade and no particular trend in the evolution of the character
emerged clearly from our analysis. It can be noted that several ornamentations
originated several times independently and most of all, from different character
states. This indicates that some transitions may occur indifferently among the
different states.
Figure 1.
Optimization of the evolution of ornamentation and of pollination in the Araceae.
Composite phylogenetic
tree of the family where each mirror tree presents the optimization of one character.
A. Optimization of ornamentation type (five character states: Psilate, Verrucate, Striate, Echinulate and Foveolate/
Reticulate). Pictures are given as illustration for each of these types, they do not correspond to a particular
species of the family. They were obtained from http://www.paldat.org. B. Optimization of pollination type (four
character states: Beetle, Fly, Thrip and Bee pollination). Species names are coloured according to the subfamilies
(Orontioideae in pink, Monsteroideae in blue, Lasioideae in orange, Calloideae in green and Aroideae in red).
The last common ancestor of the group Areae+Arisaemateae is indicated by a red arrow.
