Pollination & seed dispersal

[droseraholic]

Hi,

I have been sowing various winter-growing Drosera recently (D. cistiflora, peltata, macrantha ssp planchonii & whittakeri - wish me luck!  

), and was struck by how different the various seed structure/morphology is in this genus: from the tiny D.cistiflora, through the small rounded peltata, to the what I can only describe as "wierd" D.macrantha ssp planchonii, to the (relatively) huge D.whittakeri seed! Also, from experience other members of the genus are different again (e.g. the fusiform [=thin at either end, swollen in the middle, like a giant orchid seed] shape of D.rotundifolia).

Has anyone ever done a study to see how they are adapted for dispersal in the wild? e.g. D.rotundifolia may be partly wind disperal (but not v.far range I think), D.whittakeri dispersed by insects perhaps (e.g. ants), etc. Most probably just fall near the parent plant in (hopefully) suitable soil. It just struck me as an interesting question!

Also, similar question re: flower pollination. For example, many pygmy Drosera seem to have almost a "metallic flaked" appearance, which is extraordinarily beautiful to us humans (IMHO) - is this also an adaptation to specific insect pollinators?

Most studies on CPs seem to generally concentrate on the aspect of carnivory, but I think these other aspects are also very interesting, especially if we wish to understand their biology in full.

(Of course, the same questions can be applied to other [lesser] CPs as well - ducks & runs!! )

Just a couple ideas I thought I'd kick around!  

Adam.

 

[Tamlin Dawnstar]

I have read theories that mention the distribution of many of the Australian droserae, like sarraceniae in the U.S., follows along a "hurricaine alley", and that the presence of Drosera peltata in Asia is a result of the seed being carried by strong winds there (Robert Gibson, pers. comm.)

The seed of the tuberous species is specifically adapted for long dormancies. This seed is large with abundant endosperm, and may remain viable for many years where it falls, until the frequent Australian fires clear the surrounding vegetation which offers competition. The heat/smoke stratifies the seed, often leading to mass germination of various species. Chemicals in the smoke are dissolved out of the air with rains, and are carried to populations outside the range of the actual fires, resulting in germination of this seed as well. Dispersal of this seed is probably done mostly by water carrying the seed via streams in the wet season, as the seed is quite hefty as seed goes in this genus.

For the other species with smaller seed, wind and water are the predominant methods of dispersal. Long flights by migratory birds carrying seed on their feet is also suggested.

The metallic appearance of some of the pygmy species might be a relic from the days when populations were still experiencing sexual reproduction, possibly as an attractant for a specific pollinator which is no longer needed as most species now reproduce by apomixis (without the production of seed).

These are some thoughts I have heard mentioned, but I am not aware of any research along these specific lines.

Good luck with your seed germination efforts. Don't give up if the tuberous seed fails to germinate in one season. Seed make take up to 3 years to germinate, so if you get no results, set the pots aside and try them again next season.

 

[droseraholic]

Thanks for your insight on these subjects Tamlin - very interesting!

I wonder why out of the tuberous species only D.peltata has spread beyond Australia & New Zealand? (Actually, that may not be 100% correct: as I understand it, D.insolita at least from Southern/Central Africa is also a tuberous species in sect. Ergaleium - unfortunately, I can't find much info on this species). Do most other tuberous species have larger seed, less suitable for wind dispersal in a "hurricane alley" scenario? Anyway, what you said makes sense regarding the general tuberous (and other) Drosera seed dispersal mechanisms.

As for the pygmy species, I wonder to what extent they are now reliant on apomixis. Probably to quite a high degree, as you suggest. I suppose they still rely to a certain extent on sexual reproduction: seed has quite a few advantages over gemmae, for example durability (if a population of plants is wiped out by exceptional drought, floods, or bush fires, seed is much more likely to survive), genetic diversity, and viability (seed remains viable much longer than gemmae). But of course apomixis produces many plants very quickly. So I guess the pygmies use a "two-pronged" approach for reproduction.

Thanks for your thoughts on these subjects - much appeciated!

Thanks also for the advice on germinating tuberous sundew seed. I have heard they can take a long time in some cases, although the ones I am trying are supposed to be at the easier end of the scale, hopefully! I've done a bit of research, and people use various methods to germinate them, e.g. fire stratification, "smoke water", gibberellic acid, etc. I may try one or more of these next time. I'll take your advice about keeping them aside if they don't sprout this year.

Thanks again for your help,

Adam.  

 

[carnivorous23]

Good luck with those seeds. I recently had D. peltata germinate, it took about 2 months without stratification.