From: botanist at malesiana.com (Peter Boyce) on 2008.07.29 at 06:55:20(18280)
As part of our aroid research here in Malaysia we are beginning to turn our thoughts to the age of our favourite family by, among other ways, analysing the modern distributions of related ever-wet or perhumid tropical forest herbs with restricted fruit/seed dispersal syndromes (e.g., insect dispersed short-viability seeds), such as Schismatoglottis sens lat., and then looking at tectonic plate movements to speculate about when the currently disparate taxa (or their hypothetical ancestor/s) were adjacent on a single landmass that permitted dispersal into areas that are now widely distributed (i.e., South America, Africa, the Indian Subcontinent & Sunda/Wallacea/Melanesia).
While clearly this method involves severe limitations and requires a rather uncomfortable number of assumptions about the origin and more criticall the evolutionary stability of dispersal systems, and of course much needs to be tested post-hypothesis by using more robust techniques, to date the 'results' are fascinating, to say the least.
Perhaps for us (working as we do on a group with one of the most complex inflorescence morphologies in the family, if not in the entire plant kingdom and thus using orthodoxy an 'advanced' and by inference 'recent' group) the most exciting aspect of these ponderings has been that while focus on the age of the aroids has tended to indicate that the bisexually-flowered genera with 'primitive' paleoherb growth morphology (in essence the helophytic lasioids - as championed by Hay & Mabberly) or the equally 'primitive' Proto-aroids (that is to say the Orontiodeae + Gymnostachyoideae) are basal-most in the modern lineage and, particularly given recent fossil publications on late Cretaceous orontiods giving a modern subfamily origin at least 70mya, closest in appearance to the ancestral 'protoaraceae' it now seems that the schismatoids (that this Schismatoglottis sens lat.+ Cryptocoryne) share a common ancestorat least 150 myo and given their modern floral complexity and their unisexual-flowered 'advanced' inflores
cences raises issues about the aroids not only in terms of whether bisexual flowers are indeed 'primitive' but also in terms of just how old IS this family.
Currently there are no indispudibly confirmed angiopserm fossils from earlier than the early Cretaceous; however already there a modern subfamily of the aroids from almost as early as the earliest known flowering plant fossils and indirect evidence that at least one modern tribe of the family has its origins from slightly earlier and THAT tribe is currently considerd to have (in modern taxa) one of the most complex inflorescence morphologies in the family.... food for thought.
Peter & Sin Yeng
| +More |
IAS on Facebook
IAS on Instagram
