Drosera Taxonomy: D.communis

Fernando Rivadavia Lopes (ferndriv@usp.br)
Wed, 30 Aug 1995 19:08:51 -0500 (CDT)

To all,

I'd like to try and clear up a few doubts about the taxonomy of
Brazilian Drosera, for myself and hopefully for others too. I know Jan
can help me and wish others would pitch in their comments.
For the past few years I've been studying native Brazilian CPs in
the wild and the biggest problem I have is that I often can't identify
them correctly, due to the confusing taxonomy of these plants. Saint
Hilaire initially described numerous species, but only a few are accepted
nowadays.
I'd like to begin with D.communis. There's one form of this
species which I call the "common form" since it seems to be very common
in sub-amazonian Brazil and apparently extends into a few neighboring
countries. It's like a small, reddish D.intermedia with long, thin scapes.
Then there's what I call D.communis "green giant". These plants
seem to occur only in S + SE Brazil and have larger, green leaves which
are usually more pressed to the ground. They look roughly like a
D.rotundifolia.
There is also what I call the "pygmy form" and the "flat red
form", both found in W Brazil. I'm not too sure if these are truly
separate forms yet though, different from the "common form", or just
ecotypes of the same taxon.
Last of all there's what I call D.sp."Emas" which has been
confused with D.communis and also occurs over much of sub-amazonian
Brazil, often together with the "common form". This new species has a
stem which may be up to 28cm in length and has narrow, oblong-linear
leaves.
Now the problem is that the TYPE for D.communis St.Hil. could be
just about any of these, I'm still not sure which. In Jan's CP
nomenclatural synopsis, he lists the following as synonyms for this
taxon:

D.communis var.alba
D.communis var.breviscapa
D.communis var.cubensis
D.communis var.pauciflora

The 1st is from Mato Grosso and probably represents what I call
the "pygmy form". The 2nd Jan puts as a synonym of D.capillaris and the
3rd simply as D.communis (meaning then that this species actually reaches
Cuba Jan?). The last is from Caraca, where I've been to on several
occasions. I've found my "common form" there, but am not sure if "g.g."
grows there. I couldn't find many of the D.communis sites I knew of while
I was there in July and on my previous trips there, I still hadn't really
noticed they were 2 separate forms and thus didn't pay attention.
I used to think "g.g" were greener because of shady conditions,
but changed my mind after finding various places where both forms grow
side by side in sunny conditions. I then noticed an easy way to identify
them, since leaf colors and shapes were variable. The petioles of the
"common form" are rounded and hairy while those of "g.g." are glabrous
and are rounded in the center but flattened to the sides. After noticing
this detail, it was even possible (though still difficult) to identify
hybrids between these 2 forms.
I have a feeling one of these 2 forms could be the TYPE D.communis
and the other var.pauciflora. I have a paper by Eichler (Eichler, A.G.
1872. Droseraceae, in Martius, K.F.von, & Eichler, A.G. Flora Brasiliensis
14(2): 385-398.) where there's a description of each Drosera species and
their varieties. For D.communis St.Hil. it reads:

"...foliis rosulatis saepius erecto-patulis lineari-v.
oblongo-spathularis obtusis, basi in petiolum longiusculum attenuatis,
supra margineque glanduloso-ciliatis, subtus petioloque glabris v. sparse
puberulis..."

While for D.communis St.Hil. var.pauciflora Eichl. it reads:

"...humilior; foliis brevius petiolatis obovato-spathulatis,
subtus petioloque glabriusculis; scapo saepius 1- nunc 2-3 floro."

According to my translations the above read:

- "...leaves in rosettes frequently openly-erect, linear versus
(=v.?) obtusely oblongo-spathulate, attenuating gradually towards the
base of the petiole, upper surface glandular-hairy, underneath petiole
glabrous versus sparsely pubescent..."

- "...smaller in size; leaves with short petioles, obovate-
spathulate, glabrous underneath the petioles; scapes frequently 1-
nunc(=?) 2-3 flowered."

Both descriptions could be applied to both of my forms, except for
the part about the petiole hairyness, which would indicate that the 1st
represents the "common form" and the 2nd represents my D.communis "g.g.".
Yet to me the information is still too vague to say for sure which is
which, if they are at all any of these 2. I have observed that "g.g."
often has more flowers per scape than the "common form", which would lead
further to pointing the "common form" as being var.pauciflora.
As to leaf shape, I understand "linear versus oblongo-spathulate"
as something like a D.anglica leaf, maybe narrower. I've seen both
D.communis forms with this leaf shape when growing underwater or invery
wet habitats, so no clue there.
The 2nd description claims obovate-spathulate leaves which I
understand as something somewhere between intermedia-rotundifolia. Again
this leaf shape can be found on both forms and leads me further to the
point that leaf shape is not a characteristic to be taken too seriously
when studying Drosera herbarium specimens, which represent only a small
sample of populations which grew in habitats usually not well specified
on exsicata.
In the wild, though, leaf shape and color are very important
characteristics when you know which factors affect leaf color (sunlight)
and shape (mostly humidity and sunlight) and how. This knowledge is often
not at the reach of taxonomists who only deal with the dead plants, not
studying the plants in the field enough (or not at all) or who don't even
attempt to cultivate the plants in hopes of understanding them better.
I'd sure like to hear opinions on the above, especially if I
messed up somewhere in the translations! At the end of this year I'm
planning to go to Europe to see TYPE herbarium of numerous CPs. I know
D.communis St.Hil. is at Paris while I believe D.communis St.Hil.
var.pauciflora Eichl. is at Munich (right Jan?).


Fernando Rivadavia
Sao Paulo, Brasil