David Hare-Scott wrote:
> Talking about sexually reproducing plants here.
> Is it true that all cultivars of the same species will be fertile with each other?
Not necessarily. Some species are by nature self-infertile and
require a second plant of the same species for fertilization (e.g.,
cherries.) It sometimes happens that some cultivars will not
pollinate others, even in the same species. For example, you may be
able to pollinate cherry A with Cherry B, but not with Cherry C.
Also, many cultivars are sterile polyploid hybrids and can't
effectively pollinate anything.
> Can different species cross-pollinate and produce fully functional and > fertile offspring?
Yes, but usually they must be very closely related, and it doesn't
work with everything. For all intents and purposes, this doesn't work
at all in animals, which is what makes defining species boundaries so
much easier in animals than plants. Plants are much more tolerant of
disruption of their genetic material. There are even multi-*generic*
crosses possible among orchids.
> Talking about cabbages.
> In my supermarket there are cabbages (4 kinds), broccoli , cauliflower, brussels sprouts and Asian vegetables (about 8 kinds, buk choy, choy sum, wong buk etc) that all look like members of the cabbage "family" to me. Are these all cultivars of one species, all different species, or several species and cultivars of those species?
Broccoli, cabbage, kale, cauliflower, kohlrabi, and brussels sprouts
are all members of the same species, Brassica oleracea, each selected
to emphasize a different part or trait of the plant. When you get to
Chinese cabbage and bok choi, you are dealing with other species of
Brassica (different reference books will list different species names,
as the group has undergone some revision in recent years.)