Topic of the Week--Woody Irids

Martin Grantham
Sun, 20 Jul 2003 22:36:05 PDT
Some Experiences with South African Woody Irids

The South African woody irids are a fascinating and little studied group of 
plants in the Iris family that can grow to be true shrubs producing 
thickened woody stems that arise from woody caudices. The largest species 
and the one with the longest cultivation history, Nivenia corymbosa, can 
exceed nine feet in height with a woody base more than a foot and a half 
across! There are three genera: the monotypic Witsenia, Klattia with 3 
species, and Nivenia with 10 species. All have leaves in two ranks making 
stiff fans of foliage along flattened stems. The genus Patersonia in 
Australasia shares many features with the South African woody irids and may 
be their closest relatives. Patersonia also produces woody growth, but only 
in underground stems. The previous genera along with Aristea and Geosiris 
have all been placed in the subfamily Nivenioideae within the Iridaceae 
based primarily on the pairing of the basic irid flowering unit, called a 
rhipidium, to form binate rhipidia.
I am growing the following species:
Nivenia corymbosa
N. stokoei
N. binata
Witsenia maura
Klattia flava
These were grown from seed either purchased from Silverhill Seeds or shared 
with me by friends in South Africa. I grow them all with similar care. The 
free draining soil mix I use includes fine peat, coarse peat, Felton sand, 
and pumice. I top dress with a layer of pure pumice. I feed with Dr. Greens 
fertilizer distributed by E. B. Stone in Sasoon, CA, but I think fish 
emulsion or kelp fertilizers would work as well. These plants produce a 
large root mass for their size and a relatively large pot is in order. The 
roots like to be cool, so a black pot hit by full sun can be a problem. I 
never allow the soil to dry completely between waterings. The plants 
appreciate bright light and good air circulation. Beyond the seedling 
stage, the only pest damage experienced has been a bit of nibbling on the 
leaves by cucumber beetles.

The definitive reference to the South African woody irids is Peter 
Goldblatt's beautifully illustrated 1993 monograph entitled The Woody 
Iridaceae, published by Timber press. Dr. Goldblatt has since published an 
additional species of Nivenia, N. parviflora, in Bothalia, 27,2: 101-103 (1997)

Now I'd like to share with you some of my experiences with a few of these 
plants beginning with the genus Nivenia, plants with flowers in exquisite 
blues to rival the gentians. These wonderful blue flowers are produced in 
the heat of the summer by 8 of the species and in the spring by 2. 
Individually flowers last at most 2 days in sun, but each inflorescence can 
produce flowers in clusters over several weeks. Numerous inflorescences are 
initiated over a period of a month so that they are out of phase, 
prolonging the flowering period which can be up to 2 months. Cut 
inflorescences in water continue to flower for a month or more. Fires 
occasionally burn plants back to their woody bases and they can resprout 

Nivenia corymbosa is the largest, best known, and longest grown of the 
woody irids. I first saw flowering plants in 1989 while a horticulturist at 
UC Berkeley Botanical Garden. Former UCBG Director Dr. Robert Ornduff had 
grown plants for studies on heterostyly. N. corymbosa is one of the 6 
heterostylous (more exactly, distylous) species in the genus, meaning that 
individual plants produce either long-styled flowers with short stamens or 
short-styled flowers with long stamens. These were typical "post research" 
plants in that they were underpotted and filled with weeds. They still 
flowered wonderfully with many 5/8 in. deep blue flowers with white 
throats. The soil was a light, sandy clay and much of it pushed out by 
copious root production.
Later, while briefly in charge of the African Plant collection, I was able 
to find that these plants are easily rooted from cuttings of vigorous 
shoots direct from the caudex, treated with low level rooting hormone, and 
stuck in a 50/50 peat and sand mix with bottom heat. Cuttings from 
flowering plants can flower themselves in one or 2 years from rooting and 
go on to develop a basal caudex just like a seedling. In 1995 at the end of 
a work/study program funded by the International Plant Propagators Society 
I was able to see plants in habitat at Bainskloof in western South Africa 
with Rod and Rachel of Silverhill seeds. I ordered seeds of 3 species from 
Silverhill that year: N. corymbosa, N. stokoei, and N. binata. I also 
obtained seed of Witsenia maura via friends from Betty's Bay. Planted 
without special treatment in the fall of 1995, these seeds followed a 
germination pattern which indicated they might have a seed dormancy. 
Germinants appeared in the fall of 3 successive years. I later made tests 
of N. corymbosa that indicated aged seed germinated well (near 50%) without 
special treatment, that a GA3 soak at high concentration could increase 
germination about 10% and make it occur earlier by a week, and further that 
smoke extract alone delayed germination about a week. Seedlings proved 
susceptible to two problems in a greenhouse: spring aphids seems to illicit 
an almost toxic response with yellowing and rapid death at moderate levels 
of infestation, Botrytis (grey mold) attacked the first senescent leaves 
and progressed into the stems. Both problems might have been lessened by 
growing outdoors in higher light where the young plants would produce a 
tougher cuticle. I ended up with 15 plants from my first sowing of C. 
corymbosa, now 8 years old. The largest has exceeded 4 ft. in height and 3 
ft. in width and is producing 50 inflorescences that should flower in Sept. 
Only 3 of the 15 plants have become competant to flower as yet so this 
species can have quite a long juvenile period.

Nivenia stokoei has the largest flowers of the genus up to 1.5 in. across 
that vary from pale silvery blue to deep blue. It is not heterostylous. The 
foliage is quite waxy glaucous. It grows in a limited coastal area in and 
around the Kogelberg Biosphere Reserve. Out of 5 seedlings from 1995, all 
were competant to flower within 5 years and 3 flowered within 4 years, so 
this species appears to have a shorter and more uniform juvenile period. 
The largest plant has reached 2 ft. in height and 2.5 ft. in width in 8 
years. When grown under artificial light the flowering time can be shifted. 
This species also appears easily propagated by cuttings treated as 
described above. Seed germination has been poor.

Nivenia binata blooms in the spring with flowers that range from pale blue 
to dark blue and up to a little over 3/4 in. across. The branching pattern 
of the inflorescence brings the flowers nearly into a single plane It is a 
heterostylous species. It grows in the Swartberg Mountains over a range of 
conditions. Out of 4 seedlings only one has become competant to flower in 8 
years. The largest plant has reached 2.5 ft. in height by 2 ft. in width. 
Seed germination has been poor in several attempts.

I had the opportunity to see N. argentea and N. stenosiphon flowering in 
habitat last Dec. They were growing in a harsh environment in the Rooiberg 
Mountains which are in the middle of the Klein Karoo. Heading up out of 
succulent scrub there is an interesting transition to a fynbos community 
and near the top of the formation the woody irids appear. N. argentea is 
striking with silvery bracts around the large flowers of an extraordinary 
blue. It grew both in exposed areas and under dense shrubs. N. stenosiphon 
was generally growing directly in cracks in rocks and showed many charred 
branches from previous fires.

Witsenia maura is a plant of wetlands and fairly low elevation. It has 
large flowers (almost 2 in. long and over 3/8 in. wide) that remain closed 
with bright yellow, beak-like tips, a green zone which intensifies almost 
to black and then fades to yellow again at the base. The flowers are borne 
in conspicuous pairs that mature at the same time. The stigma protrudes 
from the tip like a snake's tongue. Out of 4 plants from a 1995 sowing, all 
have flowered in 8 years with the first flowering in 5, so this plant 
appears to have a relatively short and uniform juvenile period. Despite a 
nutrient poor soil mix, the plants I'm growing do not stand erect as I've 
seen them in the wild. They are growing in a way that I interpret as the 
result of too much nitrogen and must be staked. Germination is reported as 
good and I think I sowed under 10 seeds to get 4 plants. The tallest has 
reached 6 ft. in 8 years, but would be lying on the ground without its 
stake along with its numerous basal branches.

Klattia flava is not the star of the genus, but a few seeds have yielded 2 
small plants at this time that appear to be doing quite well. It is 
reported that Klattia gradually regresses and dies in cultivation, but this 
may be based on plants dug from the wild rather than grown from seed. The 
most desirable plant in this genus would be K. stokoei because the leaves 
below the fringed head of flowers turn a bright scarlet and hold that color 
for a long time after flowering. It is a most beautiful plant that grows in 
the coastal region in and around the Kogelberg Biosphere Reserve. I know 
some South Africans are trying to grow it and hope they will be successful 
in its cultivation.

Picture Links:

Nivenia stokoei
My photo of habitat in Kogelberg Biosphere Reserve…
and another good link for this species:…

N. binata:… 

Klattia stokoei and K flava, find beautiful pictures of them on this list 
in Missouri Botanical Garden's Tropicos database:

Witsenia maura flowering photographed at San Francisco State University by 
Dr. Bob Patterson…

I will be selling Nivenia corymbosa plants at the Harland Hand Memorial 
Garden 9-7-03 and hope to have a flowering plant on hand. Check out this 
event at:

Martin Grantham 7-20-03 

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