Tropical African Gladiolus

John Grimshaw
Thu, 08 Mar 2007 23:46:48 PST
Mary Sue wrote:

>Although they don't talk of species in central Africa, when I
was doing the thumbnails for Gladiolus and trying to decide how to split
them up there was one on the wiki that was in that area with a photo
supplied by John Grimshaw,  Gladiolus watsonioides:…

>Perhaps it's a candidate to be included in the hardiness test group.

There is of course the companion volume by Goldblatt, Gladiolus in Tropical 
Africa (Timber Press 1996), covering the 82 species recognised by him at 
that time. Of these a few species overlap with those covered in 'Gladiolus 
in Southern Africa', but the majority are rather local in their 
distribution. The principal exception is the ubiqiuitous G. dalenii, found 
throughout subsaharan Africa (and Madagascar) except in the densest 
rainforests or driest deserts. It extends northwards to the mountains of 
Yemen and western Saudi Arabia, and thus makes the nearest approach of an 
'African' species to those of Eurasia (which all look rather similar and 
have pink/magenta/violet flowers). There is a hint in Goldblatt's book that 
its distribution may have been assisted by humans. On the lower slopes of 
Kilimanjaro it is a weed of arable fields and in fallow years can flower 
abundantly, colouring areas orange. Like Chris Whitehouse, my experience 
with unadulterated G. dalenii has not been very satisfactory, as it flowers 
too late in the year. Clones such as 'Boone', which may or may not be 
hybrids, are much more reliable. I have, however, recently been sent new 
material of G. dalenii that might be more satisfactory.

G. watsonioides is the highest altitude Gladiolus (up to 3900 m, 12,800' on 
Mt. Kenya) and quite capable of withstanding nightly air frosts. The problem 
with it in cultivation is that it doesn't have a defined seasonal cycle and 
can be in growth at any time of year (although it usually flowers for me in 
autumn). I know people in the British Isles who attempt it outside, but I 
think a very sheltered site is needed for success. I should think that the 
San Francisco bay area would ideal with its cool summers & mild winters.

There are several other red-flowered Tropical African species of which I've 
seen G. longispathaceus and G. abyssinicus in the Bale Mountains of southern 
Ethiopia. The latter has curious narrow tubular flowers with a large green 
bract behind them, one of several species throughout Africa with such an 
adaptation to bird pollination.

The most important commercial species of Tropical African origin is G. 
murielae (Acidanthera murielae of catalogues) with a scattered but wide 
distribution from Ethiopia to Malawi. It is not reliably hardy in the UK. In 
the same section (Acidanthera) is the beautiful, pure white G. candidus, 
which can be abundant in grassland in the East African highlands. I would 
love to spend time investigating the pollinators of these two species, as I 
suspect that G. murielae shares a pollinator with Impatiens tinctoria (both 
have large white flowers with a purple centre and delicious evening perfume, 
and a very similar range), and in Tanzania G. candidus grows in the same 
grasslands as the pure white Delphinium leroyi, which is also beautifully 
scented. The two are similar in stature and flower size. All of these 
potential partners in pollination have a long nectariferous spur or perianth 

John Grimshaw

Dr John M. Grimshaw
Sycamore Cottage
Nr Cheltenham
Gloucestershire GL53 9NP

Tel. 01242 870567

Easter Monday 9 April, Arboretum Weekend 15-16 September
Gates open 1pm, last entry 4 pm

More information about the pbs mailing list