species that form turions

[Apoplast]

Hello all - I have been thinking about turions a lot recently. As in more than I'd like to admit to. One of the things I have been wondering is if someone has created a master list of all of the utric species that can form turions? Here "can" is the operative word. For example, the wide ranging species U. gibba can be grown year round and does great in the tropics. But, I have to imagine that the populations in my home state which can experience -30C every winter must produce turions to survive. Is that accurate? If so, then I would consider U. gibba as a species that can produce turions, even if all populations don't.

The real question for me is species that are subtropical in habitat in their higher latitude populations. Like does U. foliosa produce turions? It ranges into Texas where occasional snow can fall. Okay very occasional. Still, the water temps must drop enough that it would induce turion formation in other species. In these locations, does this species just grow through the winter? Are there papers on this out there that I just couldn't find? I'd love to hear from anyone with any broad knowledge of aquatic utrics. I'm looking at you Barry. This seems like you - lists and utrics! But I'm sure I am overlooking others with lots of knowledge too, because I don't yet know the aquatic utric community well. So to those I've overlooked, please excuse my ignorance.

[ICPS-bob]

Good question. I wonder if Andreas Fleischmann might know. Or perhaps Miloslav Studnicka, Martin Spousta, and Jan Franta who rumored to be preparing a three volume "Utricularia - Atlas of Bladderworts" (at least that is what was printed in the June 2012 issue of CPN 41(2):82).

[adamcross]

Hi Apoplast - turions are highly modified hibernacula, but are still essentially an adaptive response to unfavourable conditions. Theoretically, the capacity to produce turions should be universal across all aquatic species (as for many other aquatic genera), with expression determined by environmental factors (and perhaps buried under local adaptation in some populations). The only other method of persistence through these periods (excepting dispersal over landscape scales) is the development and maintenance of an extensive sediment seed bank; something not widely observed for aquatic Utricularia.

As an example- U. australis and U. gibba grow extensively throughout the arid-tropical Kimberley, where water is generally present in permanent billabongs and the like for most of the season. I've collected barely wet mud samples from these areas just before the onset of the wet season and found plants persisting buried in the sediment. Seedlings of both species also come up from sediment samples, though in low numbers. Turions aren't necessary in this environment, however both species will readily form turions in colder environments (south-west WA) in response to the onset of winter. I've seen U. australis turions literally choking a wetland near Esperance in late winter. I gather both species are also known to produce turions naturally in New Zealand, and U. australis will over east as well.

[Apoplast]

Hi Bob - Thanks for the suggestions! I don't know that I read about the potentially forthcoming volume on utrics. I'll have to go back and take a look.

Hi Adam - Thanks, although I'm well aware of that turions are. I'm not sure I agree that all aquatic plants form turions. In fact I am pretty sure they are not all capable. In my experience with different Myriophyllum species there has been variation between species in their ability to form turions.

But back to Utricularia. Even within the genus I very much doubt that the development of turions is an ancestral trait. Given that the most parsimonious hypothesis for the ancestral physiognomy of utrics, considering the present phylogenentic data, would be a tropical terrestrial. Neither of these characteristics would suggest it likely had a developmental program for turions. Even within sect. Utricularia, there are a number of tropical species. I haven't grown them yet, but suspect these species are probably incapable of forming turions.

To me, all of this suggests that there should be variability within the genus for the development of turions. I don't even know, does U. purpurea form turions? I would guess yes, but I haven't found information on it. I'm just curious if someone has amassed this information, particularly in as publicly available dataset.

[adamcross]

Apoplast, I meant the capacity to produce turions is theoretically universal within the aquatic representatives of the Utricularia (as for other aquatic genera where turion production is a common trait), not that all aquatics are capable of producing them- you're quite right in that this is certainly not true!

Your point about the tropical ancestry (edit- within the Utricularia) is also true, however assuming that turion production is not an ancestral trait would imply that it has evolved numerous times in different geological areas to resolve a common ecological problem. My hypothesis would be that an early ancestral aquatic species developed the capacity to form turions, likely as an autoecological response to periods of much cooler climate (similar to Aldrovanda), and that subsequent dispersal/speciation into new areas in recent geological history resulted in species that either express the trait (temperate and sub-tropical), or do not express the trait (tropical) in response to climatic requirements. It is well established in the literature that aquatics display extensive ecophysiological plasticity and high local adaptivity, and equally well established that many characters are present but deeply buried in apparently non-expressive species.

As with all hypotheses, I may well be completely wrong! I wouldn't be at all surprised if Utricularia were a complete exception to aquatic flora generally. However, from my work with aquatics over the last few years, the above hypothesis is what the literature (in general) would suggest.

[Apoplast]

Hi Adam - Thanks for clearing up your point. I think I see your argument now. Before I respond though, I would like to thank you for your proper use if the word "hypothesis" rather than the vernacular "theory". I feel as though it is important for the distinction to be made when scientists like yourself speak in any public forum.

I presume your second paragraph relates exclusively to Utricularia, and the evolution of turions within that lineage rather than across multiple aquatic plant lineages. I do believe that the evolution of turions has occurred multiple times within angiosperms as it appears in both monocots and dicots. It is possible that there was an aquatic ancestor to all flowering plants if you follow Carlquist and colleagues' interpretation. I, however, think there is far better evidence for Feild and colleagues' interpretation of the characteristics of early angiosperms. That aside, there are similar arguments for the production of tubers and succulence across lineages that seem well supported morphologically and genetically. So who knows what mysteries will be discovered this point.

Returning to Utricularia, you may be correct that they had an aquatic ancestor, but the current roster of species and relationship to Genlisea doesn't seem to provide strong support for that. Your argument does make me wonder how terrestrial utrics survive winters in extreme cold. Our few species here must freeze solid, but I don't know in what state they survive these conditions. That may be at least part of the answer. I'll have to look into that.

Regardless, I still hope to find out if anyone has a list of species of utrics that either can express turion development or can't. Maybe the capacity to express turion production is the difference between tropical/sub-tropical species and the ones that survive into temperate/boreal zone. Just a thought.

[coline]

Apoplast, as reffering to making the list of the ones able to make turions, if there were no lists made, why not start to build it here, lets say one of the first posts to be edited and species added there after the formation of the turion is confirmed and discussed in the further posts if there was any doubts?

[Apoplast]

Hi Coline - Not a bad idea. I'm still holding out hope of finding someone with a list. If I find a publicly available list, I'll post it here.

[leeb]

I haven't seen such a list.
You might have to go through Taylor's monograph using the index and the species descriptions to compile one.

It would be interesting to know what sections of the genus Utricularia turions are found in; this would say something about whether they evolved once or multiple times in the genus.

LeeB.

[Apoplast]

Hi LeeB - Does Taylor have that information in there? I don't know. I should probably get myself a copy. I completely agree it would be informative to know where turions have cropped up in the genus.

[leeb]

Well the book is around 730 pages and describes and illustrates each species, so I would expect the information to be there.
If you are lucky maybe he lists the species with turions.
Certainly you will only have to look at the aquatic and semi-aquatic species which probably means less than fifty species to check.

LeeB.

[leeb]

Okay, I did some looking around.
Firstly, all the species of Utricularia that I could find that produce turions are in section Utricularia, so it looks like the ability to produce turions evolved there.
Secondly, some tropical species at the northern or southern edges of their ranges may overwinter as seeds, in effect becoming annuals.
U. aurea, which is not recorded as producing turions is recorded from Tibet; this may be an example, or else it may produce turions but no one has recorded this in the literature.
Adam Cross mentions U. gibba producing turions above, but I was not able to find mention of this elsewhere; and Bruce Salmons book on N.Z. carnivorous plants mentions it doesn't grow turions in N.Z.; so not everything is recorded in the literature, or at least not that which I could access this afternoon.
U. platensis is recorded on the flora of Argentina website as occurring as far south as Rio Negro province, so it is possible that it would form turions as well, but again no one seems to have mentioned this unless it is mentioned in Taylors monograph.
The species I could find that definitely do form turions are U. australis, U. bremii, U. dimorphantha, U. geminiscapa, U. intermedia, U. macrorhiza, U. minor, U. ochroleuca, U. stellaris, U. stygia, and U. vulgaris.
So if you could get a copy of Taylor's monograph I would check the descriptions of other temperate or subtropical species in section Utricularia.

LeeB.

[adamcross]

I've definitely observed U. gibba to overwinter in the form of vegetative buds; whether these constituted condensed apical shoots or true turions I can't say for certain.

[leeb]

It's interesting that a number of aquatic Utricularia have developed novel structures that differentiate them from other species; turions are one, twelve species have radial floats at the base of their flower stalks and three species, U. inflata, U. platensis and U. benjaminiana also produce tubers.
U. stellaris is unusual in that it produces both radial floats and turions; it seems to be the most tropical of the turion forming species.
A number of the turion forming species are also unusual in that they seem to be widespread populations of sterile hybrids, propagating only by vegetative means i.e, they are clonal populations just like pygmy drosera populations growing from gemmae.
However the pygmy drosera can at least form fertile seed so they keep their genetic variability.
Yet the sterile Utricularia with limited genetic variability are widespread and successful, perhaps because they are f1 hybrids and have hybrid vigour.
The whole group of aquatic Utricularia is interesting showing how the ability to live free of the substrate was a key evolutionary trait leading to some of the species becoming extremely widespread and successful.

LeeB.

[adamcross]

Clonality and the perpetuation of a specific stable genotype are convergent characters among many aquatic species worldwide, and a common feature of most widespread hydrophytes (particularly those that are cosmopolitan and pan-tropical). The aquatic representatives of the Utricularia are somewhat of a model species for this syndrome, though generally possess a markedly narrower niche resulting from a relatively poor competitive ability (i.e. the reliance upon carnivory and subsequently diminished productivity).