S.E.WILLIAMS, V.A.ALBERT & M.W.CHASE:
"Relationships of Droseraceae: A Cladistic Analysis of rbcL Sequence and
Morphological Data"
AMERICAN JOURNAL OF BOTANY 81(8):1027-1037 (1994)
"(...) In a second analysis of 14 species of Droseraceae, 15 Caryophyllids,
one Nepenthaceae, and three Santalales, a single most-parsimonious tree was
found in which Droseraceae are monophyletic, although the position of
_Drosophyllum_ as a member of Droseraceae is only weakly supported. The
rbcL tree identified four major lineages within genus _Drosera_: 1)
_Dionaea_; 2) the _regia_-clade that contains only _Drosera_regia_; 3) the
_capensis_-clade that contains the South African and temperate species
outside of Australia; and 4) the _peltata_-clade that consists of
principally Australian endemics. A separate analysis of 14 morphological
and phytochemical characters is in general agreement with the rbcL tree
except for the placement of _Nepenthes_, _Drosophyllum_, and
_Drosera_burmannii_. A combined analysis of both data sets places
_Drosophyllum_ in a clade with _Triphyophyllum_ (Dioncophyllaceae)."
(cited from abstract)
---------------------COMMENT---------------------------
1. Although I do not share the same amount of enthusiasm in favour of
"modern molecular methods" in taxonomy with the authors, I do like most
results of this paper. I do firmly believe classifications based on
morphology (incl. cytology) and chorology can be corroborated by molecular
methods, however. And this paper is one very fine example of such
corroboration:
A) _Drosophyllum_ is a very dubious Droseracea. It is possibly even closer
to Dioncophyllaceae than Droseraceae.
B) _Drosera_regia_ is also by morphological classification a very separated
species. It clearly deserves subgeneric segregation (Alastair Culham has at
least defined a separate section for this species).
C) At least part of the Australian group ("_peltata_-clade") including
_D.binata_ and the "tuberous" species seems to be monophyletic also by rbcL
sequence comparison. I doubt a close affinity of _D.dichrosepala_ and
_D.petiolaris_ to these and to each other (l.c.Fig.2, p.1031), however.
D) The African-temperate group ("_capensis_-clade", including _D.capensis_,
_D.spatulata_, _D.filiformis_, _D.indica_) is certainly monophyletic, and
it seems so in the rbcL analyses as well. The placement of _D.burmannii_ is
not so certain.
E) _Dionaea_ is without doubt a real Droseracea. It is by no means "within
genus _Drosera_", however (see cited portion of abstract, obviously a
typo)!
(F) _Aldrovanda_ is even closer to _Drosera_ than _Dionaea_ but it was not
studied due to lack of suitable material.)
2. One drawback of the paper is the paucity of taxa studied in view of the
>>100 species of _Drosera_, but I expect we will see a more comprehensive
study in the near future (& am looking forward to reading more of this
quality).
3. I recommend this nice paper to any droseraceologist with a serious
interest in systematics. Enjoy (I certainly do so)!
Kind regards
Jan
PS: Apologies to all who I bore with my comments. I'm afraid I will not
change, however ;-)