Ants are not known pollinators of any orchids. However, ants and orchids keep a mutually beneficial relationship – a complicated process least studied in the eastern Himalaya.
It has been recorded during my work that certain species of orchid flowers attract ants even before they open. The presence of ants scare away many insects that damage or fully destroy buds and flowers while they hunt for nectar, thus affecting the process of pollination and seed production.
As flowers play a critical role in the survival of many species, orchid plants developed the system by which they attract certain species of ants with their nectar and in-turn the ants help in protecting the flowers from many damage causing insects.
It is interesting to note that those insects that cause no damage to buds and flowers are not being attacked by ants. Indeed these friendly insects are mostly pollinators of these species.
The apex (point away from its attachment) of the spur is generally pointed, round, obtuse, or rarely truncated. However, few orchid flowers produce spurs with its apex bilobed (also referred to as 2-lobed).
The reasons that make the apex of the spur unique is a topic least researched. However, it has to be believed that this characteristic is related to certain pollinator behaviour.
Generally orchids are glabrous (smooth and hairless) plants. However, hairy characteristics in orchids are not uncommon, it can be very minute to a cm long, soft to stiff, silky to shiny etc., on stem, raceme, leaf, flower parts etc. What may be, all types of hairy outgrowths are whitish.
Rarely few orchid species are with brownish hairs. It is a characteristic seen only in a few genera.
In resupinate orchid flowers, when buds are formed they are upside down – meaning the lip and spur (if present) are on top side of the bud. As the buds develop, the pedicel twists either clockwise or anti-clockwise to invert the bud, thus arranging the lip and spur to the bottom side of the flower. This arrangement helps visiting pollinators.
(Note: Pics of spurred buds are used to make the lesson more easier).
Spur is the hollow slender extension from the base of the lip. Its length and size varies from species to species. It can be a minute globose to a few cm long cylindrical structure. Spurs are often straight, pendulous or slightly curved toward its apex in arrangement.
However, a few species in genera Aerides produce uncommon perpendicularly bent triangular shaped spurs.
When all flowers bore on sides of the axil are turned to one direction, the arrangement is termed secund flower arrangement. Probably due to its rarity in the family of orchids, a few orchid species are even named after this flower arrangement with specific names or epithets like secunda, secundum, secundus, secundiflora, secundiflorus, etc.
Many observations during my field trips have opened a new dimension in the study of pollinator behaviours with respect to secund orchid flowers.
When each of the many (more than 2) flower pedicelsarises from around the same point at the tip of its peduncle, it is termed umbel arrangement. This arrangement is often compared to that of the struts (ribs/frame) of an umbrella.
Many of the species in genera Bulbophyllum are examples of this unique characteristic. Flowers in umbels are referred to as umbellate, or occasionally subumbellate (when flowers are almost umbellate).
A modified leaf considered a part of the flower is termed floral bract. The purpose of it is to support or enfold the flower, however in the case of orchid flowers it rarely enfold the flower.
Floral bracts arise from the rachis at the point of contact of the pedicel. It can be a minute triangular-like growth to a leaf-like even longer than the pedicel or the pedicellate ovary. In some species it is larger than the flower and forms a concave shape. The many characteristics of floral bracts like its length, deflexed, hairy, colours, encircling the ovary, deciduous at flowering etc., help in identifying the species.