Date: Fri, 21 Mar 1997 08:46:07 From: SCHLAUER@chemie.uni-wuerzburg.de To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1022$foo@default> Subject: Re: Drosera key ?
Dear Dave,
> In the openning of your key, you mention that you are aware
> of several short comings and unresloved problems... Could you
> tell us what these are?
1. The limits and circumscription of sects. Oosperma and Drosera are
unclear at the moment. Future research is clearly indicated and will
probably result in further subdivision. The main objective in
creating Oosperma was to formally acknowledge the IMHO tremendous
phylogenetic gap between the two temperate groups around _D.
intermedia_ and _D. rotundifolia_, respectively. This gap is rather
obscure in the tropics where hybridization and introgression may
account for many of the systematic problems.
2. The correct placement of subgen. Lasiocephala is debatable. This
group seems to share characters with all of the supposedly more
derived subgenera (Drosera, Bryastrum, Ergaleium).
3. Subgen. Coelophylla may be close to Thelocalyx. On the
other hand it may be ancestral to Bryastrum. None of these affinities
could be represented in its placement in the key for technical
reasons.
It was my aim to propose some rearrangements in the infrageneric
subdivision of _Drosera_. The relative affinities among these groups
must be elucidated by further research. Some colleagues might not
appreciate my lumping attitudes in the treatment of some taxa. But as
I have stated in the text (p.72), I think these were appropriate.
> I can speculate, however. D.rotundifolia
> (and D.anglica with it) might be misplaced in Sect. Drosera (or
> the rest of plants in the section are misplaced???) since D.
> rotundifolia's closest relatives are in Sect. Oosperma, or at
> least all the plants it has been hybridized with are. Am I headed
> in the right direction here?
I do not think so. In fact, _Drosera rotundifolia_ can and will never
be placed in a section not called Drosera because this very species
is the type of the genus, so the section (and any other
infrageneric taxon) including it *must* be called Drosera.
The plants a given species can hybridize with are not necessarily
those which are most closely related with it. But in our case, the
closest relative of _D. rotundifolia_ is _D. anglica_, which is IMHO
correctly placed in sect. Drosera, and there exists even a hybrid
between the two species. I think these are not closely related to any
other temperate species but probably derived from some now
exclusively southern taxon (e.g. the phylogenetic precursor of _D.
communis_).
> The only "error" I noticed was in the Sect. Ptycnostigma.
> Wherein, only plants with ascending stems are supposed to have roots
> thickened as storage organs.
No. The phrase "roots thickened as storage organs if stems ascending"
is meant to contrast with "ascending stem...roots not thickened as
storage organs" of sect. Arachnopus. I.e. *all* ascending members of
Ptycnostigma have thickened roots *but not all* members with
thickened roots have ascending stems ("if" but not "only if" in the
key)!
In a dichotomous key, the entries of a given branch must be compared
among each other (same level!), or else the conclusions will be wrong
as in our example.
> D.brevifolia (a flat rosette) also
> has such roots (perhaps they don't look so in herbaria?) and it
> grows exactly (well, maybe they don't flower in the same season...)
> like D.cistiflora, the only other member of the section I've grown.
> Right now, both are coming out of dormancy, and look the same:
> tiny buds growing off of the roots within a mm. or so of where last
> year's rosettes/stems were attached.
> It was rather amazing to see it! On one hand, I've got a plant
> I removed from a road side ditch as an after thought, and on the
> other, a plant all the way from South Africa (thank's Eric, it
> wasn't dead after all!) growing in the exact same manner. Cool!!! :)
Yes, indeed. Strange that previous students of the genus have
obviously overlooked these (IMHO important and systematically
significant) similarities.
Kind regards
Jan
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