Cooktown orchids.
The Cooktown orchid is found in many overlapping subpopulations in northern Queensland and
there are morphological variations between plants found in these areas.
Its naming and classification are still not settled.
Dendrobium bigibbum is now the generally accepted name but it is also seen referred to as
Dendrobium phalaenopsis, D. biggibum var. phalaenopsis, D. lithicola, Vappodes phalaenopsis
and D. bigibbum varieties bigibbum, superbum and compactum.
Because of these difficulties it is sometimes referred to as the Cooktown orchid complex.
The Phalaenthe section of dendrobiums is characterised by D. bigibbum.
Many plants seen today are hybrids of D. bigibbum and are known as den-phals because the
flowers resemble those of Phalaenopis.
Dendrobium bigibbum is an epiphyte growing in small to medium sized clumps on trees or rocks.
Green to purplish stems (pseudobulbs) are erect, and grow up to 1.2 m high and 15 mm thick.
They have rounded bases and a swollen middle section.
Young stems are covered by small papery bracts.
The 3 to 5 (12) leaves are confined to the upper part of the stem.
They are narrowly ovate and up to 15 cm long by 3.5 cm wide.
They are a dark green, often with purple at the margins or an overall purple tinge.
Normally evergreen but they can loose their leaves in the dry season.
One or more arching, leafless inflorescences arise from the top of the pseudobulb.
They are up to 40 cm long and can have from 2 to 20 flowers.
Flowers are flattish, resupinate and up to 5 cm across.
The sepals and the broader lateral petals generally curve backwards slightly.
There is a short spur.
The lip, which has 3 lobes, projects forwards.
The 2 lateral lobes curve up to surround the column.
The middle lobe is of variable length and curves downwards slightly.
Its end may be rounded or notched.
It has a prominent central ridge covered in white hairs.
Sepals and lateral petals can be shades of lilac, pink or mauve and may have a white base.
Some have almost white sepals and lateral petals.
The labellum is a darker purple.
J.F.
