|
vegetative
Orchids are perennials.
There are generally 2 modes of orchid growth patterns,
i.e. sympodial or monopodial. Sympodial orchids grow
by putting out new shoots from the base of the
former season’s organs that can be merely shoots
(ancient) or pseudobulbs (modern). Monopodial
orchids’ (Vandoideae, tribe Vandeae, sub-tribe
Aeridinae) growth points however are at their
terminal, therefore their stems keep elongating. Once
the stem is too long for apical dominance, side
shoots start to form.
Orchid leaves are generally con-duplicate (folded to
two face to face) or plicate (folded into many
pleats). Monopodials have many conduplicate leaves
because of its unlimited terminal growth. Sympodials
can have con-duplicate or plicate leaves from their
unlimited growth from the base. Each season’s growth
of stem or pseudobulb will stop after sufficient
growth. At this point, the plant can flower. In the
case of stemmed orchids such as Anoectochilus, the
stem will die back and the base will continue its
growth by producing new shoot(s) to regenerate the
plant. Some orchids such as Peristylus, Habenaria
and Pecteilis have tubers instead. Paphiopedilum
have very short stem and new shoot arise from its
base without the sacrifice of the previous shoot.
Modern orchids with sympodial growth produce swollen
base of the stem to form a structure very much
indeed like a bulb. Pseudobulbs however are more
permanent and will only die back to produce new
growth if conditions are very unfavorable. It is not
uncommon to have orchids forming clumps, clusters or
trails of pseudobulbs. Some pseudobulbs are very long
indeed, such as the stem of Eria and Dendrobium that
do not die back any part of it when supporting next
season’s growth. Sympodials can have one leaf (Bulbophyllum,
Dendrochilum), two leaves (Coelogyne), several to
many leaves (Paphiopedilum, Anoectochilus,
Eria,
Dendrobium) and a lot of leaves (Podochilus,
Appendicula, Agrostophyllum) per shoot or
pseudobulb. All these shoots or various forms of
stems will be considered as analogy of pseudobulbs
from this point onwards. |
