| dc.description.abstract | Cupressus lusitanica Mill. is grown as an exotic forest
crop in Kenya for softwood timber production in compensatory
plantations. In the Kenya Highlands it is the most successful
exotic softwood, ana timber produced annually from thirty
years old plantations already exceeds that produced from the
dwindling reserves of indigenous softwood forest which they
were planted to replace. It provides a valuable export
product.
In cultivation a preferred form of Cupressus lusitanica
has arisen which shows superior growth, straight lightly
fluted boles, simple fine branching and low susceptibility
to Monochaetia canker. It has been suggested that this form
has arisen by hybridization of Cupressus lusitanica with
C. macrocarpa Hartw. and, perhaps, with other species.
The history of the introduction of Cypresses is outlined
and it is shown that, if Kenya Cupressus lusitanica iso
hybridized, possible male parents are New World strains of
C. lusitanica from Central America, Cupressus macrocarpa
Hartw. from Monterey. and, less probably, Cupressus
torulosa Con or ~ arizonica Greene.
The formal taxonomy of the genus Cupressus L. is briefly
reviewed and it is concluded that eleven species of Cypresses
may be recognised, four in the Old World and seven from the
New World. Delimitation of species in the genus is extremely
difficult because cypresses are very variable trees showing
a wide range of vegetative form within one species.
Examples of extreme variation in vegetative form in Kenya
. .
and in Costa Rica are given, emphasising the difficulty of
taxonomic discrimination in this genus.
The specific status of Cupresstls benthamii Endl. from
Mexico and Cupressus lindleyi Klotsch (now considered to be
respectively a variety of, and synonomous with, C. lusitanica
~ill.) from Northern Central America has long been disputed.
The historical and herbarium evidence for their being
conspecific with Cupressus lusitanica Mill. is reviewed.
,
Biometric evidence from cones collected from native stands
in Mexico, and studies of the progeny of Bentham's cypress,
both in Mexico and in Kenya, established that this tree can
only be regarded as a variety of lusitanica. The American
origin of Cupressus lusitanica (which name has priority)
and its conspecificity with Mexican trees, formerly named
Cupressu~ lindleyi, are established by re-examination of
herbarium material in both British and Mexican herbaria
and by physiological evidence obtained by Gas Chromatography
of heartwood infiltrates and of leaf waxes. The
identity of Kenya Cupressus lusitanica with European strains
of the species is established by comparison of herbarium
material, by biometric comparisons of four distinguishing
characters in Kenya crops and by analysis data of leaf
waxes.
Hybridization
The production of hybrids of lusitanica with
macrocarpa and with C. arizonica by"controlled pollination
is described. The hybrids are shown to be intermediate
between the parents in respect of vigour of growth, colour
of foliage and leaf wax constitution. Putative hybrids,
occurring naturally in Kenya, have been detected by their
intermediate appearance and confirmed as intermediate by
biometric.comparison of distinguishing features and by
analysis of their leaf waxes. Natural hybrids of Cupressus
macrocarpa with lusitanica, and with torulosa were
found. Such hybrids are nowadays rare in managed Cupressus
lusitanica crops, but are not uncommon in natural
regeneration clumps and, in the past, were more frequently
found in plantations established from carelessly collected
seed.
In a final discussion, it is argued that hybridization
has not played an important part in the development of the
Kenya preferred form of Cupressus lusitanica. This is
derived by selection from Cupressus lusitanica of European
origin, but with some interbreeding with American strains.
widespread hybridization of the crop, such as that described
by Cousens amongst Oak crop in Scotland, has not yet
occurred. With Cypresses in Kenya, hybridization is
undesirable and must be avoided. It can be avoided by
careful selection of seed sources, and this study provides
strong arguments in favour of continued work to improve the
quality of East African cypress seed. | en |
