Orchids Of The Lip

The lip is the most prominent member of the perianth. It is the highly specialized floral part of the flower and is extremely complex and variable. Sometimes it is broadly attached to the base of the column or over its entire length rigidly and therefore immobile. It may be attached to the tip of the columnfoot immovably or loosely hinged to it and is exceedingly mobile.

It may be sessil or short or long-clawed . The lip may be membranous and antrose i.e. directed upward and forwar or thickly fleshy and strongly reflexed; or may be recurved only at the tip. Very often it is porrect. The basal, middle and distal portions of a lip are often distinguishable and termed as hypochile, mesochile and epichile respectively. The hypochile is occasionally laterally stetched backwards as a lobe known as auricle.

The lip may sometimes be undivided and then usually concave, ventricose, cymbiform  porrect. Occasionally as in Androcorys pugioniformis, the unlobed narrowly oblong-triangular lip with a broad base is excavated into two deep oval, parallel pits. More often it is divided into three or more lobes or segments, commonly at the base. Very often the lip is divided at the middle or at the apex. The outer lobes are known as the lateral lobes or sidelobes. The lobes may themselves be entire, lobed or deeply divided. The lobes or the segments of the lip may be broad. The lateral lobes may be erect or spreading. It may be entire (Pachystoma) or of fimbriate to filiform segments .

Sometimes the lateral lobes of the lip or the entire are convolute, embracing the column and giving the lip a trumpet shape. Often the lateral lobes are short and indistinct. The midlobe may be large and spreading  or small and tongue-like (Pecteilis). It is generally entire or sometimes divided into two The edges of the midlobe are often wavy, recurved or crisped Sometimes the lip is deeply bifid or two-lobed at the apex as in Listera pinetorum, Neottia listeroides etc. But at times it is bibbed along the length as in Cephalanthera damasonium. The space between the lateral lobes is termed as disc.

The inner face of the lip, especially at the basal region or on the disc, is provided with decorations of various kinds that are intended to serve as guide-markings on the landing platform  for the pollinators. These surface features are growths usually in the shape of longitudinal crests , keels , lamellae or may be of various kinds of thickenings or rows of papillar warts . The form of the callosities may be simple but may be occasionally complex. In several species like Eulophia graminea, Pleione hookeriana the outgrowths are in the shape of fat hairs along the veins. Occasionally there are movable hairs, which catch slightest movement of the wind.

The lip at the base may have two lateral tubercles or knobs without other decorations on the lamina. The upper surface of the lip becomes papillose, as in many species under Bulbophyllum, Cirrhopetalum, etc. Sometimes as in Monomeria longipes, the lip is very puberulose, the distal half densely and shortly stiff hairy. Often the lip is provided with coloured markings, blotches or stripes.

The lip may be variously shaped like a boat , a funnel , a slipper or shoe. The base of the lip is often variously saccate or has a sac-like to tubular extension — a hollow appendage, called the spur. It usually bears glandular tissues inside and secretes sectar dear to the insects.

The spur is variously shaped like globose , conical , clavat, straight or bent to strongly curved forwards . It is shallow as in Chiloschista, Geodorum, and Thrixspermum; deep, basin or jug-shaped as in Gastrochilus and Pomatocalpa etc.; long tube-like as in many Calanthe, Habenaria etc. Sometimes it is short and hidden by the lateral sepals or conspicuously long upto and In a few cases like the terrestrial Corybas, Satyrium or the epiphytic Diplocentrum the lip has two collateral spurs.

The spur is often provided inside with calli at the bottom; papillae and glands, stalked or not ; hairs warts or with various other projections on its back or front walls Cleisostoma, Pomatocalpa, Staurochilus. Rarely it is septate or has a fleshy transverse growth at the mouth of the opening. These thickenings or projections on the inner side of the spur furnish important characteristics for identification. In Cottonia peduncularis, an epiphytic vandaceous orchid from peninsular India, and extending to Sri Lanka, the lip in its structure, colour and texture remarkably resemble a certain bumble-bee. This is a typical case of mimicry — a feature not uncommon with orchids.

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