"The most unusual Xanthosoma is X. atrovirens from Ecuador. It has two very
peculiar forms, one with flaps of tissue like small leaves on the underside
of the leaf ('Appendiculatum'), and the other with long-tailed pouches at the
apex of each leaf ('Variegata Monstrosa'). Similar excrescences to those of
'Appendiculatum' are found on certain taro (Colocasia esculenta) cultivars
such as _Piko lehua apii_, but the pouched form is probably unique in the
Araceae.
What purpose could these pouches serve? Many plants in the rain forest have
downward pointing 'drip tips' which assist in shedding rain from the surface
of the leaf. If the leaf stays wet for any length of time, evaporation from
the pores (stomata) is hindered and the plant has a circulatory problem as
then it cannot draw in water and nutrients from the ground. Wet leaves also
impair photosynthesis and make the leaf surface prone to colonization by algae
and other epiphytes. Drip tips are even more important for species which hold
their leaves almost horizontally in order to intercept as much light as
possible. But instead of shedding water, X. atrovirens 'Variegata Monstrosa'
must actually collect it.
It has been said that in spite of the intense competition, the tropical rain
forest is the soft option for plants in that it does not take much to merely
survive where there are no stressful seasons, prolonged droughts or cold
spells to weed out the weak and raise the threshold of survival adaptations.
In such an environment even freaks stand a good chance and the occasional
freak may eventually turn out to have a feature which comes in useful. And so
the monster of one epoch becomes the new species of the next.
The connection is inescapable: the pouches of X. atrovirens 'Variegata
Monstrosa' look like the pitchers of insectivorous plants. Without fossil
evidence we cannot be sure how carnivorous families such as Sarraceniaceae
evolved but one theory is that they arose as a result of scyphogeny, the
freak cupping of leaves. Then, as water and debris such as dead insects
collect in the sacs a nutrient solution forms which provides a foliar feed
for the plant. In poor soils a plant with this deformity would therefore have
an advantage. With this scenario it is amusing to surmise that this Xanthosoma
could be a proto-insectivorous aroid!"
Steve
SAMARAK@UAFSYSB.BITNET or SAMARAK@UAFSYSB.UARK.EDU