Field of Science

Gneater (neater) than all get out!

Visits to our teaching greenhouse still manage to deliver surprises even thought I have been doing it regularly for years.

This is something the Phactor had never seen before: the ovulate strobilus (cone) of Gnetum (knee-tum). Hmm, that's pretty funny, telling you how to pronouce a silent G with a silent K.

Gnetum is a tropical liana, and that's one of the reasons I've never seen strobili before. They're usually way, up, there. The closest I've come before is the seeds, mature ovules, which are about 4 cm long. They have a fleshy, reddish outer seed coat that attract and reward an animal disperser. Finding these seeds on the rain forest floor means that somewhere far above where the vine clamors along in the canopy, a strobilus just like the one above got pollinated.


The strobilus consists of several whorls of small bracts (modified leaves) above which is a whorl of ovules. Ovules are not eggs so their name is a misnomer. Ovules are jacketed, indehiscent megasporangia. The single megaspore produced develops into a haploid female (a gametophyte) who then produces an egg. The jacket prevents the pollen access except through a small hole. The ovules shown here are ready to receive pollen. The ovule has exuded a a drop of sticky liquid out through this small opening and any pollen grains (endosporic males) that adher to the surface of this pollen drop get pulled inside the ovule when the ovule reabsorbs the liquid.

This is not the work of a passive female. She reaches out, grabs passing males, and pulls them into her lair.

Now if the foregoing description wasn't a tipoff, what makes Gnetum so Gneat is that this is a gymnosperm, a relative of conifers, albeit a fairly distant one. Yet as you can see, this vine has broad leaves, and it has vessel elements in its wood, both features usually associated with flowering plants. And of course there is a certain flower like quality to the strobilus.

Do flowering plants share a common ancestry with Gnetum? The jury is still out. For many years data suggested that the answer might be yes, but most recent studies suggest this strange plant is more closely related to conifers, and not in a gymnosperm lineage having a common ancestry with flowering plants.



3 comments:

Mona Albano said...

Neat! The fruit looks like a pecan; I don't suppose it is, though.

Have they looked at the DNA of that ancient Australian Wollemi pine-clone compared to this?

Dr A said...

No pecan; Gnetum.

Wollemi pine is closely related to Araucarias, monkey puzzle trees and hoop pines.

Gnetum is more closely related to Ephedra and Welwitschia, two other very strange gymnosperms.

Sally said...

Thanks for giving us a chance to see and learn about this unusual plant! The oddballs are always my favorites for some reason...