Mary Sue Ittner msittner@mcn.org
Mon, 10 Nov 2003 14:50:39 PST
This introduction for the topic of the week from Robin Attrill got filtered 
out by the our server and I have no clue why so I am forwarding it on.

Mary Sue
Dear all,

Amongst many gardeners Oxalis tends to be rather stigmatised by the 
occurrence of a few weedy taxa amongst the many hundreds of species which 
constitute the genus.  Fortunately there are also a very large number of 
desirable species which merit a place in cultivation.  The majority of 
these are geophytes, predominately native to Africa and the Americas, and 
it is these plants that I will introduce in this weeks TOW.

The most extensive number of species, and diversity of form, occurs in 
South Africa, principally in the winter rainfall regions. These plants, 
which flower from August through to April in the northern hemisphere, occur 
in an extraordinary range of habit, leaf shape, and flower colour, examples 
of which are illustrated on the PBS Wiki at 
http://pacificbulbsociety.org/pbswiki/index.php/…. We are indebted to the 
late Michael Vassar, whose enthusiasm for these plants, and generosity in 
distributing them, has done much to popularise oxalis as a whole. A 
selection of desirable, and easily grown, species includes O. orbicularis 
(early flowering lilac blooms over very attractive foliage with purple mid 
ribs and fringes to the leaflets), the O. flava complex (very variable leaf 
shape and flower colour, typically yellow but also white and lilac), O. 
hirta ( variable flower colour from almost crimson, in the form 
'Gothenberg', to almost white), O. versicolor (white flowers with crimson 
on the reverse giving a candy stripe effect when in bud), O. massoniana 
(orange with a yellow centre), and, towards the end of the season, O. 
obtusa which possesses probably the most variable flower colour of all with 
the range encompassing pinks, oranges, yellows and white. I find the best 
means of cultivation is in pots, kept dry in summer then thoroughly watered 
in autumn after which they are watered on a needs basis throughout the 
growth period during which they are kept frost free (minimum 5 celsius). 
The potting medium should be well drained, and not too rich otherwise 
foliage will predominate at the expense of flower. These plants require 
excellent light to prevent etiolation. If plants are grown in open ground 
those species which produce bulblets at ground level (which disperse 
readily) should be sited with caution.

A second group consists of the 'alpines' from southern South America. Three 
species are widely available and generally not difficult to grow - O. 
adenophylla, O. enneaphylla and O laciniata - all of which are very 
worthwhile either in pots or in a rock garden. These come into growth in 
late winter and flower in spring and early summer.  A considerable number 
of species occur further north in the Americas but rather few of them are 
in cultivation.

Identification of Oxalis tends to be a rather difficult process due to the 
paucity of recent literature. As mentioned by Dave Victor in a posting a 
few weeks ago, there is a Checklist, produced by Richard Clifton of the 
Geraniaceae group (ISBN: 1-899742-43-3), which assists in sourcing the 
literature associated with the named species but it does not contain keys. 
The only handbook on the Southern African species, by Salter, is almost 
sixty years old - a reprint was produced by Rainbow Gardens Bookshop a few 
years ago but I do not believe it is still in print. Copies of the original 
are virtually unobtainable as the print run was very small. Despite these 
difficulties many of the un-named plants in cultivation do have associated 
collection/accession numbers  - particularly those originating from the 
Vassar collection - which can be used to provide information on their origin.

Sources of Oxalis material are widespread but rather few in number.  In the 
USA they include Telos Rare Bulbs(http://www.telosrarebulbs.com/index.html) 
which offers a good selection, and the PBS exchange lists contain some 
excellent plants from time to time.  In the UK Monocot Nursery lists a 
small but interesting selection. Remarkably -and unfortunately! - the 
number of suppliers in South Africa is extemely limited but Cape Seed and 
Bulb (http://www.clivia.co.za/) offers a small selection. In contrast to 
bulbs, seed is rarely available - a combination of generally limited 
viability and exploding seed capsules makes it a rather difficult 
proposition  - but the Flores and Watson seed lists sometimes contain 
interesting South American species.

In summary I believe Oxalis to be a genus with great potential.  The plants 
require little space and are generally easy to grow.  They provide a 
beautiful flowers throughout the year in a range of colours that is 
difficult to match amongst the monocot geophytes.  Why not try them????!


Robin Attrill

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