Biomedical Engineering Reference
In-Depth Information
Table 4.1 The subgenera of
Salix
, the willows, and their uses
Common
name
Subgenus
Typical species
Uses
Chamaetia
Nasarow
Alpine and
Arctic
willows
Ornamentals
Longifoliae
Andersson
New World
willows
Salix exigua
Salix
Tree willows
S. alba, S. babylonica,
S. daphnoides
Ornamentals, frost protection,
and cricket bats. Occa-
sionally biomass (pulp and
bioenergy)
Vetrix
Dum
Shrub
willows
Sallows,
S. aurita
,
S. caprea
,
S. cinerea;
and osiers,
S. purpurea
and
S. viminalis
Basketry, hurdles, biomass
(pulp and bioenergy)
also been used in breeding,
S. alba
and
S. daphnoides
in particular, but for many
species there appear to be incompatibilities and/or crossing barriers between mem-
bers of
Salix
and
Vetrix. Salix triandra
has historically been classified as subgenus
Salix
until recently when AFLP analysis of 154 accessions from the UK National
Willow Collection placed it between
Salix
and
Vetrix
[
5
].
S. triandra
has been a
useful parent in European breeding programs and freely hybridizes with
S. viminalis
in nature (creating
S
.x
mollisima
). Within
Vetrix,
interspecific hybrid-
ization is widespread and routinely exploited in breeding. The extent of natural
interspecific hybridization within subgenera has traditionally made willow classi-
fication very difficult. These uncertainties in
Salix
taxonomy account for how
variable the estimates of numbers of species within the genus are.
Willow ploidy ranges from diploid to the atypical dodecaploid.
Circa
40 % of
the species in the genus
Salix
are polyploid [
6
]. Breeding programs commonly
exploit a range of ploidy levels from the common diploid up to hexaploid. There are
several cultivars that are sterile triploids, the result of diploid x tetraploid crosses.
Despite the historic association of humans with willow, it has not been necessary
to subject willow to domestication until relatively recently. The enormous diversity
of wild forms has served the past needs of human beings well. Prehistoric human
populations in northern Europe built simple boats (coracles), and the Romans made
fine, delicate woven willow baskets; Pliny the Elder (AD 23-AD 79) advised on
willow planting in his extensive “Natural History.” Those first willow plantations
were probably made up from the selections from the wild for characters such as
multiple branch-free stems, flexibility of stems, and potential to regrow after
cutting. As willow constructions, particularly at the scale of domestic containers
(baskets), became more popular, bark color and ease of stripping bark would have
also been considered.
Mechanical harvesting did not become widespread until the later part of the
twentieth century by which time agronomic practice was being used to render
growth habits more suited to the machines available. Specifically, practices such
Search WWH ::
Custom Search