August/December 1997 
19 
12.000 species of plants widely distributed 
throughout the world in many habitats. Most are 
found in the southern hemisphere. It is believed 
they evolved in a world that was considerably 
wetter and warmer than the present, as a result of 
which they maintained a dependence on the water 
environment for their growth and reproduction 
(Rodger, 1974). In addition to high humidity, the 
ferns of the modem world thrive in shaded places 
especially under tree canopies or in rock crevices 
and stream banks. But they have other specialised 
features that make them competent to exploit various 
environments. We shall briefly describe some 
reproductive features and then adaptations for 
growth. 
Reproduction 
Most ferns need an extended period of surface water 
availability for spore germination, gametophyte 
growth and gametic transfer. The exceptions are 
those which have un underground gametophyte 
Because the sexual process is so chancy, vegetative 
reproduction has been developed repeatedly. Some 
have small bulb-likc lumps (called gemmae ) on their 
fronds that can be brushed off by passing animals, 
others can root front frond tips. Many mitt out the 
necessity for sex by producing asexual ( 2 n ) spores 
Spores of primitive ferns arc larger and their dispersal 
from spore sacs less efficient, therefore they are often 
found in open, windy places. Ferns growing in the 
water have developed separate male und female 
spores and gametophytes. which do not develop 
into autonomous plants. Possibly the reason for this 
is the rapidity with which water levels rise and fall, 
but it serves to show how adaptable the terns are. 
Growth 
Ferns grow slowly compared with flowering plants 
and need special strategies to overcome this 
competitive disadvantage. They can grow where 
flowering plants find difficulty in totally covering 
wet soil, or where their light spores can beat a heavy 
seed in the race to a suitable temporal^ site. They 
are easily destroyed by breakage or grazi ng. Few arc 
lough enough lo withstand trampling but most arc 
poisonous or glandular, and contain no starch in the 
leaves making them unattractive to herbivores Ferns 
have apparently found it easy to become 
poikilohydric. that is. capable of drying without 
dy ing and there are more of such plants in East Africa 
'han in wetter climates. They are found in places like 
••alls and cliffs, which arc usually dry but very wet 
«ner the slightest rain. Other adaptations to dry 
conditions are hairy coverings, and fronds that break 
op and fall when water becomes short. The form of 
5»c (sporophyte) plant is important. Tufted fronds 
vound an upright stem (rosettes) are good at tapping 
1 -ght in shaded conditions, while spaced fronds along 
a creeping stem are good at invading grassland or 
clinging to surfaces. 
Habitat Conditions and adaptations 
In these notes the reader is referred to Faden ( 1994) for 
descriptions of fem families and genera. There are no 
descriptions in Johns’ (1991) check list. 
Terrestrial Habitats 
On the forest floor, most ferns are rosettes with small spores 
in efficient spore sacs for weak air streams. Flowering plane 
are unable to hlanket the soil in these low light condinom 
Common genera here include Arplwium. BuHteUtt 
Dnvpterls. pterls . but there are many others 
Rock crevices with protected bare soil and limited tree w*xr 
period arc suitable habitat for other species many of 
having poikilohydric rosettes. Although rock cr ***** c» 
often in full light they can resist invasion by 
plants on the first-come-first-servcd principle am 
hold the only pteridophytes in dry country and 
common here are ActiniopterlS and Pellaea 
Streamsides have bare soils through water erosion, quickri 
exploited by masr.ive fem fromls. The tree ferns {Cftfhts 
spp) and those with large spores (Maraitla and the 
Thelypteridaceoe) can grow here. In adjacen' swam pi 
competition from flowering plants is intense but can be 
overcome by creeping stems nnd large fronds. 
Disturbed grasslands can contain conspicuous creeping 
ferns each plant of which covers a large area, wresting B 
i he rarity of sexual reproduction. The bracken fem 
Pti-rldlum aquilinum. is a worldwide weed in such grazing 
land. Hvpolepis is common in these habitat* at high© 
altitudes. Alpine rocks are an important habitat for ferru. 
which arc adapted to low temperatures, such at 
Anogramma. Potvs He hum and Woods la. 
Epiphytic habitats 
Hie surface of branches and irunks of forest trees have 
limited free water availnbility but are open habitats with 
mure light than on the soil Tlicre is a wide range of iniowc 
so we find a mixture of rosettes and creepers, large ar-j 
small spore bearers, water demanders and drought 
tolcrators. Species of the family Polypodiaceae ore major 
players in this habitat, including the Sing’s Horn Fem 
Plalvcerium which is uncommon in Kenya but often 
cultivated. Ii has stalkless, clasping leaves like elephant's 
ears, which gather soil against the tree trunk, and erect 
branched fronds bearing the missed spore sacs. Asplettium 
is a common epiphytic genus on moist forest ireev In the 
wettest forest, specie* of the delicate 'filmy fem* . 
Hynienophvlluni and Thchnmuncs. are often found hanging 
from tree minks or rocks by water. 
Aquutic Habitats 
Specialised ferns float or are submerged in water of pond* 
and shallow lakes and streams. They are invariably creeping 
and often successfully outgrow all other plants, such 
the rails of Salvlnia moUsta on Lake Naivosha and 
