>Now the clincher... has anyone put forth any erudite speculation=
on how
>the genera in this family evolved?=20
>There is an "interesting" article in
>CPN from a few years back. In it a guy claims to have all the answers..
>If you are familiar with the article, you can understand why I was=
not
>convinced! :-)
>
>-Michael
IMHO, the greatest problem in Lentibulariaceae evolution is the open
question why the assumedly most "primitive" species of _Utricularia_
(sect.Polypompholyx and sect.Pleiochasia from Australia) do not occur in
the region where all three genera overlap in their geographical ranges
(Central America). In the light of this, I think the progenitor of the
genus _Utricularia_ should have looked like the Australian species
mentioned above but its range should have overlapped geographically with
that of _Genlisea_ (I think _U._ evolved from _G._, and _G._ from
_Pinguicula_). This should have happened sometime before Miocene. As the
continents were quite separated at that time already, the genera (in the
first line _U._) must have spread dramatically over the globe *after* they
were separated genetically from each other. At least in some species, there
must have been some considerable long distance dispersal. But as propagules
of _U._ (seeds, turions) can definitely be transported by birds, I see no
great barriers to this. If we accept this, the situation may have been as
follows:
46irst, some strange plant of Scrophulariacean origin, having glandular
hairs on its leaves (and living in nutrient-poor, assumedly moist
environments), inhabiting some piece of land in the region that is now
Central America, has "decided" to become carnivorous (by the step-by-step
acquisition of digestive properties), which made it possible for the plant
to utilize the insects +/- frequently trapped by the glandular surface of
the leaves. By chance, this species had free central placentation and two
stamens (the other Scrophulariaceae don=B4t have this combination of
features), to help further taxonomists recognize the newly forming family
Lentibulariaceae 8-). Thus, _Pinguicula_ was born. This genus may have
developed the strange single-flowered flowering habit and refined the
rosetted way of life (forming hibernacula as a response to boreal or alpine
climate). But sometime before this, the _Genlisea_ progenitor must have
split off. As this genus doesn=B4t seem to have managed to conquer habitats
different from those of its assumed origin (restricted to tropical zone),
and shows quite uniform morphology in all species, maybe the modern species
are quite close (morphologically and geographically) to their immediate
progenitors. The links between _G._ and _P._ are completely extinct
nowadays 8-(. Thus, it remains a mystery how the elaborate trap leaves
developed. On the other hand, there are dozens of possibilities to suppress
roots. Maybe, the racemous inflorescence is a "primitive" trait in
Lentibulariaceae (thus, _Pinguicula_ is more "advanced" in that respect).
_Genlisea_ should have managed the jump from America to Africa and
Madagascar after its complete isolation from _Pinguicula_ (_P._ does not
occur in Tropical Africa). From the still rather "primitive" _Genlisea_,
some steps which must have run parallel (but are not as mysterious as the
_P._->_G._ step, viz. formation of the still more elaborate suction traps,
fusion of sepals) have led to _Utricularia_. The immediate progenitors of
which must have overlapped in their range with _G._, as mentioned above.
Because this isn=B4t the case nowadays, I think they have become extinct in
their original range (I do not think _Genlisea_ had a broader range than
nowadays).
_Utricularia_ has both shown the greatest diversification of growth types
(diffusion of differentiation), and the greatest spread over the whole
globe. As certainly, long distance dispersal must have occurred repeatedly,
it will not be too easy to construct all paths of evolution within this
genus.
I am convinced that
1.Lentibulariaceae is a natural, monophyletic family.
2.All genera of Lentibulariaceae are natural and monophyletic.
3.The evolution started from _P._ progenitors and passed through _G._ to _U._.
4.The most primitive Lentibulariaceae are extinct now (even _P._ shows
advanced traits), there are no real links between the genera at hand.
5.We know far too little to be sure of any of the speculations above!
Kind regards
Jan
PS:Some of the above looks pretty like teleological reasoning, but be sure
that I do not believe in a directed evolution. It was just used for
illustration of those "steps" in evolution which were indeed composed of
several subsequent mutations.