Re: Jan's Drosera Dichotomous Key

Fernando Rivadavia (ss69615@ecc-xs09.hongo.ecc.u-tokyo.ac.jp)
Wed, 6 Nov 1996 14:33:55 +0900 (JST)

Jan and all,

>> >Chorological reasoning indicates such, however. The W half of S AM
>> >(especially Colombia and Ecuador) is excepted; rather unusual for a
>> >recently formed area (which should be more continuous).
>>
>> Explain better please, I didn't understand this part.
>
>_D.anglica_ (recent spread) does not have large gaps in its total
>range (except where expected: oceans, dry regions, &c.).
>Thelocalyx has one besides the Pacific Ocean: the whole W of tr. S
>AM. And this region is not devoid of _Drosera_.

OK, so you're saying that species which spread recently are more
likely to not leave gaps behind in their ranges, while species which
spread longer ago are more likely to leave gaps, such as the one found
between D.burmanni and D.sessilifolia (Africa, that is). So where do
Colombia and Ecuador come in this story?

>> Just like we prefer to assume that no reversals occured, I'd say
>> it's better to play safe and say that if two "ancient" species were
>> separated for such a long time, they would be bound to be very different
>> in the end, due to unevitable accumulations of mutations. And considering
>> how uniform these 2 species are in their respective ranges (well,
>> D.burmanni not as much maybe), I would suggest a recent spread, such as
>> that which occured with D.anglica.
>
>The difference does not need to be larger than between the two
>species of _Mitrastema_ (Rafflesiaceae, E AS and Mexico) or the three
>spp. of _Langsdorffia_ (Balanophoraceae, one each in Madag., N.Guin.,
>and Mexico to S Brazil). These disjunctions are also generally
>believed to be old.

Sorry Jan, but I don't participate in the Rafflesiaceae nor the
Balanophoraceae listservs, so your examples were lost on me and most other
here I'd imagine.

>You should know him, as he is a scientist who takes the time/does
>the work others obviously don't before he starts publishing. He is
>(the) one author from AU (Adelaide, I think) I know of who has
>published some well researched papers on _Drosera_ recently. They are
>certainly worth reading.

Which??

As to D.subtilis, summing it up, it is thus the only member of
subgen.Ergaleium which is native to N.Australia. Apparently it has not
been collected with tubers and is thus probably rare. I think I remember
Allen Lowrie saying (in 1993) that he had never been able to find this
one.

As to D.tokaiensis you say it shouldn't be considered a species
because it is limited to the range of the parents. Yet I don't understand
how you can say it is not independednt from the parents and compare it to
D.X obovata. The latter is also obviously a hybrid, but it has 2n=30 and
is incapable of reproducing sexually. Thus it only occurs where the 2
parents occur side-by-side or nearby.
On the other hand D.tokaiensis has a full set of chromosomes from
D.spatulata and another full set from D.rotundifolia and is completely
reproductively independent from the parents, existing where one or both
parents are not present. Furthermore, hybrids with either parent are not
viable. It thus has an unique genome which is free from the ancestors and
can follow its own evolutionary path. So where's the problem?

Best Wishes,

Fernando Rivadavia
Tokyo, Japan