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Thread: South African Droserae

  1. #57

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    The posted examples of D. dielsiana and D. collinsiae conform to what I know as the typical species. I am still betting that the plant in the photo is D. madagascariensis, but I can't make out the stipules in the photo. Time will answer this question for sure.
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    Talking

    Hi, here is a plant of mine i think is the real D.burkeana,

    what do you all think?


  3. #59

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    There are several key features to Drosera burkeana that are often overlooked by collectors claiming to have this species in cultivation. I have found this to be a frequently misidentified species in most collections. Here is a synopsis of the species which I hope helps you with your plant.

    Drosera burkeana has a petiole length which is quite abbreviated. Laundon, in “Flora of Tropical East Africa” gives the petiole length as 2-20 mm. Obermeyer, in “Droseracae of Southern Africa” states the petiole is about equal in length to the lamina c. 1 cm. I believe the short petiole is a very distinctive feature in determining Drosera burkeana. The petiole is equal sided and straight for its entire length. In cross section the petiole is round (terete), and somewhat hairy on the upper surface.

    Details of the scape include a glandular pubesence over the entire peduncle (“omnia pilosum” per the protolouge).

    The leaf is suborbicular, not quite round. The lower leaf surface is glabarous.

    Sepals are irregularly serrated at the top, and glandular.

    Flower details are fairly unreliable since the plant has many affinities regarding the styles to other species, and flower color is variable.

    The best diagnostic for determining this species would be the details of seed testa: seed is 0.2 -0.4 mm long, 0.15 – 0.2 mm broad, oval with slightly pointed ends, shiny, black and smooth, with pits in the seed coat. Of all these details, the pits in the seed testa are the most conclusive.



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  4. #60

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    Hello,

    My Drosera dielsiana flowers at the moment. Here are two photos of the flowers of the plant, you can see in the photo i posted above. It's the big plant on the right hand side.. The flowers have been opened only for about 1 1/2 hrs in the early afternoon.

    I removed the photos from my Webaccount! Who wants to see them, can send me an Email. I will send you the pictures then.


    Christian

  5. #61

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    Hi Christian,

    Those are beautiful flowers, but I question the identity of D. dielsiana based on the repeatedly divided styles which are more typical of plants in the Drosera aliciae/natalensis complex. Although repeatedly divided styles (not simply bifurcated from the base) are occasionally found in D. dielsiana, they are rare.

    Here is a photo I consider to be more typical regarding the bifurcation of the styles.

    The smaller rosetted plants in your photo are likely to prove closer to D. dielsiana. As I mentioned earlier, D. natalensis and D. dielsiana are closely allied taxa. D. dielsiana was separated from D. natalensis by Exel and Laundon on the basis of seed shape and length. The seeds of D. dielsiana were described as “ovoid, 0.3-0.4x0.2 mm” vs. those of D. natalensis described as “ellipsoid-fusiform, 0.5-0.6 mm long …0.2 mm broad." I assume this rather precise measurement was used to divide the two taxa in the area where their range overlaps, and introgression produces too many phenotypes for floral criteria to be effective.

    Drosera dielsiana has been successfully hybridized with D. nidiformis and D. natalensis, and since the F2 generation is likewise fertile, the possibility of different forms is endless.
    ("sp. Durban" and " sp. 4 South Africa" are likely to be 2 of them)





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  6. #62

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    I have been cautioned by my mentors not to place any ultimate reliance on the various taxonomic keys for the process of species determination. Field work and herbarium study is essential to understanding the nature of these populations.

    For most of us, the literature is all we have to go by, and it is solely from my own experience with my plants, and from the various published keys that my comments are drawn, along with some very helpful education from Dr. Jan Schlauer, Robert Gibson and Vitor Olivera de Miranda that I base my comments on.

    In reply to my question of "Just how reliable is the information found in the various published keys?" Robert Gibson had this to say in reply:

    "Botanical knowledge is iterative, so even the best keys and
    descriptions are dependent upon the nature and extent of the collections behind them and the authors knowledge of the living plants. So most keys and descriptions come unstuck somewhere along the way. Also, treatments
    like Obermeyers were based on specimens in only part of the range, so may give a false impression where other variants exist further afield.

    What is "typical" technically comes down to the type collection(s), which has inherent dangers if the collections are old or poor, not to mention that they may prove to be atypical to the rest of the population that is given the name from that type! Then there are also seasonality factors that can cloud the issue further, e.g. small compact rosette in
    the dry season and large, luxuriant rosette in the wet season." (Robert Gibson Pers. Comm. 031603)


    I like this comment as well, made by Dr. Jan Schlauer:

    "The reason for the seemingly non-scientific (or non-exact) nature of taxonomy is that there are no nearly as finite, constant, and well-defined items in vivo as in litteris. Taxa are theoretical concepts constructed by the human mind, not the things that really exist and happen in nature. You may regard this insufficient and error-prone (and you are right&#33[img]http://www.**********.com/iB_html/non-cgi/emoticons/wink.gif[/img], but I think (and I know many colleagues agree here) it
    is the only way to think and to communicate about these natural beings and processes among humans. Our mind is not prepared for more complex analysis and comprehension. This is why names and their proper use are so important for most of us..... Mankind has tried to find a precise, general,
    and reliable species definition for many generations without appreciable success. The crux is "species" do not really exist out there. Living beings are not constant."



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  7. #63

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    Hi Tamlin,

    On our german board we also had a discussion about some of these sundews. The photo from above (the plants, not the flowers) was shown by another member, and I was told to have a form of Drosera dielsiana that is near to Drosera venusta.

    I'm very interested in pictures, that show the flower details of these species. If someone has a good picture, it would be great if you could email them to me, or post them here.


    Christian

  8. #64
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    Hi Tamlin,

    As per request here are some close-ups of the plant, a little sharper this time. The stipules are quite evident.

    [img]http://home.**********.com/noah/glabripes.JPG[/img]

    and some close-ups.

    [img]http://home.**********.com/noah/closeupofglabripes.JPG[/img][img]http://home.**********.com/noah/closeup2.JPG[/img]

    I think the there are enough stipules present to point to a positive identification as Drosera glabripes. What do you think? From what I can see in the close-ups (my bare eyes can't on the plant) the stipules seem to branch, as you described.

    -noah




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