How does your garden grow?
By Eric Danell, Dokmai Garden
Here we see
the orchid fruit en face. Left of the guardian ant’s abdomen is the pit of
the column apex where the pollinia used to be. All sepals and petals
including the lip are still present, but will be discarded.
It is a privilege to be able to grow
native wild orchids in their natural climate outdoors. Although the flowers
are spectacular also in a greenhouse on another continent, such an orchid is
disconnected from its natural habitat.
An interesting observation in Vanda liouvillei (Orchidaceae) is that the
buds seem protected by ants, just like in Duabanga, peony and many other
plant species. The orchid buds must exudate compounds of interest to the
ants. If it was plain sugar ants would crawl on all nectar-rich flowers, but
they don’t, so the attractant might be quite complex. Then, when the flowers
open, the attraction disappears because the ants are sporadic or absent. The
absence of ants during its flowering stage makes sense, because an open
flower must invite its pollinating insect, not have it killed by ferocious
ants. After pollination and successful fruit formation (I am still unaware
of the pollinating insect) the ants are needed again. The ants are attracted
to the vulnerable young fruit, which must be protected from hungry insects,
mammals and gastropods. When the fruit is dry and mature, the minute
dust-like seeds disperse by the wind. Recently I rubbed an entire ripe fruit
of a Vanda denisoniana orchid to the rough bark of a Pterocarpus macrocarpus
tree. It will be interesting to see if that results in any future seedlings.
If any of our readers would like to make a contribution to science, kindly
bring a chair, a camera and some snacks to try to document the pollinating
insect. It is likely to be a diurnal organism due to the colours of the
flower. We have a net to catch it with (a voucher specimen is needed). At
present there are some 150 flowers left but only two fruits. This year we
have many more specimens blooming of this species. Through hand- or natural
cross-pollination between genetically different individuals we have also
successfully acquired fruit formation in many Dendrobium orchid species,
including the precious Dendrobium albosanguineum. www.dokmaigarden.co.th.
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