Dendrobium is a large genus in Orchidaceae (the orchid family). Depending on which classification system you follow, it is either the largest genus in the family or the second-largest, second only to the genus Bulbophyllum. Most dendrobiums are epiphytes, plants that grow on trees but do not prey on their host’s food supply. Instead, they derive their water and mineral nutrients from whatever the wind and the rain bring to them.
The three sepals are as colorful as the three petals.
As is true of orchids in general, the dendrobium flower has a calyx, a cuplike structure consisting of three colorful leaves called sepals. Three equally colorful petals rest within this calyx. Two of the petals are similar in form, while the third, called the labellum, differs from the other two. "Labellum" means "lip," and the labellum of the dendrobium is indeed an elegantly lobed liplike structure. Its exact form varies from species to species.
You can see the column on the flower to the right.
A structure called a column or, more formally, a gynostemium lies within the petals. It consists of a fusion of the male and female parts of the flower. On top of the column is a sort of canopy that contains the pollen, while the stigma, the female part that receives the pollen, lies further down the column. Unlike the column of the hibiscus, the column of the dendrobium is not a cylinder but a semicircle, the open end of which faces the labellum.
Two of the dendrobium’s three sepals lie near the labellum, one on each side. These two sepals unite with each other to form a structure called a mentum. "Mentum" means "chin," and it does indeed jut downward from the bottom of the flower like a chin. This structure is a distinguishing characteristic of the genus Dendrobium.
Insects pollinate orchids.
Dendrobiums depend on insects for pollination. Some attract insects by their fragrance, others by visual attractions. The labellum serves as a landing platform. When the insect enters into the heart of the flower, it inevitably leaves with pollen packets called pollinia clinging to it. If the insect visits another dendrobium of the same type, it will inevitably leave the pollen on the sticky stigma.
Dendrobiums have rhizomes, which are horizontal stems, often not very long. From this rhizome a new upright stem shoots up year after year, so that the old growth and the new growth rest on the same structure. This growth habit is called "sympodial growth."
The vegetation of dendrobiums assumes a variety of forms. None have the underground bulbs that occur in some genera. Some have pseudobulbs, which are wide, thick stems of varying length. Besides providing support for the leaves, the pseudobulbs can store water. Other dendrobiums have cane stems instead of pseudobulbs.
Dendrobiums have true roots with tissues similar to those of other flowering plants. But instead of growing in the ground, the roots of epiphytic dendrobiums anchor the plant to a tree branch or trunk. Other dendrobiums are lithophytes, the roots anchoring the plant to a rock. Dendrobium roots obtain water and mineral nutrients from material that falls on them.