Proposed plant regulations - defence of Oxalis

Christiaan van Schalkwyk
Mon, 27 Jul 2009 14:27:52 PDT
Sorry guys, Lou's post finally provoked a response from me, and admittedly, 
a skew one !

He said: but there may well be some species with a history of invasive 
behavior that should legitimately be banned even in small lots of seeds. 
Think Oxalis. I could spend hours every day cleaning Oxalis out of my pots 
and they would still return. They must have started from only a few seeds. 
Some plants do deserve to be banned.

This is nonsense. One cannot make a rule affecting a whole genus because of 
a skew understanding of the genus as a whole or because of the presence of 
an unruly few, an idea which I think has been suggested in previous posts. 
One does not judge a whole family by glaring down on the blacksheep, each 
and everyone to his own merrit, please!

In defence of Oxalis

The genus Oxalis have a few (my guess is less than 10 -please correct me) 
possible invasive BULBOUS species, and disregarding the 250 + low or zero 
risk species is not making much sense. And probably the one Lou is trying to 
eradicate is one of the Oxalis corniculata group (smallish creeping and 
crawling plant with small yellow flowers). It does not have a bulb, it can 
self pollinate (very few Oxalis do, in fact it's only the "weedy" or shrubby 
species which does), and its a native American spread right across the 

In my experience (that is, my garden) all invasive Oxalis are american 
species (I even suffer with two forms of O corniculata, and you are bound to 
get O. latifolia now and then with a nursery bought plant), so you (USA) are 
still stuck with them, even if you ban all others !!
Admittedly, Oxalis pes-caprae has taken foothold in many parts of the world, 
but IT STILL DOES NOT SET SEED, and can be perfectly contained in a pot if 
you realize how it spreads. Old potting soil needs to be sterilized or 
soaked with systemic weedkiller before dumped in the garden or refuse heap 
in order to kill all bulbills.
And most of the other bulbous species have such strict pollination rules 
that even by careful pollination might not yield any seeds (once again, 
there are exceptions).
Some species can produce copious amounts of axil bulbs, and some of these 
(eg. those of O pocockiae) are very light and can be carried away by water 
to a nearby area. Once again, understanding the species will allow you to 
make right decisions, and the axil bulbs can be easily destroyed when still 
unripe. How many of these axial bulbs actually grows into maturity is still 
a good question.

So to make a rule about a genus which have a few (my guess is less than 10) 
possible invasive bulbous species, and disregard the 250 + low or zero risk 
species is not making much sense.

For some point of reference:
I have currently more than 500 pots with Oxalis, featuring some 380 species 
and forms
Last year I planted 5 species in my general garden/rockery. Only one remain. 
This year I have tried about 30 species. Less than 10 grew. I'll see next 
year how many of these survived.
I have been a dedicated Oxalophile for more than six years

In my collection the only Oxalis that set seed are:
O purpurea, if I deliberately pollinate them
O obtusa, once again with deliberate pollination
O fabifolia - I have seven colour forms growing in adjacent pots. They do 
seem to propagate from the bulbs that well. The seed last about 36 hours - 
they have no endosperm. So if I do not pick them up (they are about 2mm in 
diameter - and bright green) and place them in a suitable possition and pot 
with increased watering, they do not survive.
O haedulipes - This one sets seed freely, and I am decreasing my collection 
of this species to contain only one stylar form, which will prohibit seed 
formation. In defence of this species I should add that I live right in the 
middle of it's natural area of habitat (thus right temperature, right 
pollinator, etc.), and I had about 15 different clones of it.

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