Tweedie,E. M.

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J.E.Afr.Nat.Hist.Soc. Vol.XXV No.2 (111) June 1965
PERIODIC FLOWERING OF SOME ACANTHACEAEON MT. ELGON
By
E.M. TWEEDIE
Introduction
Most species of flowering plants in East Africa flower in relation
to the rains, either before, during, or after, but there are some which
flower at very long intervals, and then ~ masse. This phenomenon has
been noted before, and is well known in the bamboo (Arundinaria alpina
K. Schum.), where the interval between flowerings has been estimated
to be as much as 40 years (Wimbush 1945). Again, Fey (1964, p. 55)
states "This plant, known to the Kikuyu as Songoya (probably Mimulopsis
solmsii Schweinf.) is of particular interest •••• Its life span is
nine to ten years during which it grows to a height of about twelve
feet. It then produces a profusion of pale mauve flowers ••••• " Fey
mentions that the plant last flowered in 1953 on the Western Aberdares.
As far as I know, no one has tried to find out why these plants
flower at such long intervals, and it might be possible to stimulate
interest in this curious and widespread feature of our highland forest
plants by records of flowering. Few people have systematically
recorded flowering times in East Africa and it is as a contribution to
our knowledge of this subject that I write these notes.
Observations
From 1948 to April 1964 we lived on the north-east slopes of
Elgon near the forest boundary. Near the house was a patch of untouched
virgin forest. I found it was carpeted with a tangle of plants with
soft dark green leaves, and when they flowered I collected the
following:-
These all flowered regularly each year, but I noticed among them
a plant with very different leaves, which did not flower. Each year it
grew taller and eventually flowered in December 1952 and January 1953.
It proved to be Mimulopsis solmsii Schweinf. By then it was five feet
tall and much branched. The flowers were white with a pale brown
throat, and came out irregularly a few at a time. The inflorescence
was covered with dull red sticky glandular hairs. It flowered in a
mass over the whole forest at an altitude of 7,500 ft. to 8,200 ft.
and smothered the usual undergrowth Acanthaceae completely. Eventually
it died down, and its dead stems covered the ground and all the usual
herbaceous plants were buried beneath it. Towards the end of the rainy
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Periodic Flowering of some Acanthaceae on Mt. Elgon
season young seedlings appeared among the rotting stems, and more in
the early rains the following year. By the end of 1954 the usual popu-
lation of Acanthaceae had taken over, though in rather different
proportions. Then the plants of Mimulopsis solmsii with their distinc-
tive leaves began to appear again. In October 1961 they began to
flower, and there was a mass flowering as before, followed by a similar
dying down, and reappearance of the usual plant population. This gives
a nine-year interval between one flowering and another, but I shall not
be there in 1970 to see if the interval between flowerings is regular.
There is another plant growing on Elgon from about 8,800 ft. to
the upper edge of the forest, which also flowers at intervals.
Mimulopsis cf. qlandulosa (Lind) Bullock non Bak. is rather like
M. solmsii in habit, but its flowers are larger and a pretty mauve
colour, with a yellow flash on the lower petal and a white throat,
darker inside. The stem, calyces and pedicels are covered with dark
reddish hairs and it grows to four or five feet. It has one peculiar-
ity, that quite short stems which have been hacked off beside the
track or grazed off just outside the upper edge of the forest can
still produce a few conspicuous mauve flowers. In January of 1947
when I was ascending Elgon it made a sheet of bloom allover the upper
part of the forest. Further mass flowerings occurred in the dry
seasons of 1956 and 1964. I also collected it in 1951 but am not sure
if that was a mass flowering or only an isolated plant, such as occur
very rarely between the mass flowerings. I did not, however, make
such careful observations as I was able to do with M. solmsii owing
to the distance of the locality from my house.
Mimulopsis arborescens C.B.Cl. is also to be found on Elgon. It
is a large plant ten feet tall, with leaves up to nine inches across.
Its flowers are cream with a chocolate brown throat and they turn
brown when they die. This plant is rare in the area of which I have
experience, but it is conspicuous. It is only recently that it has
occurred to me that I do not see its flowers every year. I have not
had the opportunity to make a continual study of this plant, but I
think it would be found to flower at intervals like the others.
I have found the same behaviour in two species of Isoqlossa. In
the spring of 1951 I sent a specimen to Kew (891) which may prove to
be a new species. When asked for more material I had the greatest
difficulty in finding it again and regarded it as a rare plant until
in January 1953 it made a mass flowering in conjunction with Mimulopsis
solmsii and it did the same in the dry season of 1961 to early 1962,
again in conjunction with M. solmsii. It has the same soft dark leaves
and herbaceous habit as the commonAcanthaceae of the forest under-
growth but it is the only one among them to have this mass flowering
at intervals. It has a white flower with light brown markings on the
petals.
Thirteen miles from this patch of forest is the bridge over the
Suam River, where the same sort of forest comes down to 7,000 ft. in
the valley of the Suam. Here in September 1959 I found a plant of
Isoqlossa oerstediana Lindau which I had never seen among the
Acanthaceae of my own patch of forest. When visiting the same place
in October 1963 I noticed that this plant was making a mass flowering
in certain parts of the forest near the river. At the same time I
found quite a number of these plants in my own patch of forest where I
had never seen it before, but not enough to be considered a mass flower-
ing. It has the same habit as the other Acanthaceae of the forest
93
J.E.Afr.Nat.Hist.Soc. Vol.XXV No.2 (111) June 1965
undergrowth; the flowers are white shaded with pink and with very small
dark maroon calyces.
Summary.
Periodic mass flowering has been recorded in Kenya, but dates are
rare. Years of mass flowering may be separated by years during which
there are no flowers, or flowers may be merely rare in the interval.
The following species and dates of mass flowering for Elgon have been
recorded in this paper.
Mimulopsis solmsii Dec.1952 - Jan. 1953.
Oct.
- Dec. 1961.
Mimulopsis cf. qlandulosa
Jan.475
Jan.
64
arborescens
3 pr bably periodic but not
recorded.
Isoqlossa sp. (Tweedie 891) Dec. 1952 - Jan. 1953
Oct. - Dec. 1961
Isoqlossa oerstediana Oct. 1963. probably periodic but not
recorded.
References.
FEY, V. (1964) Cloud over Kenya, Collins, London.
WIMBUSH, S.H. (1945) The African Alpine Bamboo. Emp.For.J. 24: p. 33 -
39.
(Received 2nd June, 1965)
94


Periodic flowering of some Acanthaceae on Mt. Elgon

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Periodic flowering of some Acanthaceae on Mt. Elgon

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