This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
This delicate orchid has preserved no record for us of its antiquity. It is, however, an Arctic plant found in the N. Temperate and Arctic regions, in Arctic Europe, and Siberia. In Great Britain it grows in every county except the Isle of Man, Peebles, Shetlands, and so ranges northwards to Sutherland elsewhere. It grows at 1900 ft. in N. England, and in Ireland and the Channel Islands.
The Tway-blade is a common clay-loving plant, growing in open fields and meadows, in moist hollows, both in upland and lowland districts. It is also exceedingly abundant in damp woods, growing side by side with Man Orchis, Red Campion, and other shade plants in the depths of woods, copses, and plantations. Tway-blade has a tall, graceful, slender stem, with fibrous root, the stem being clammy, with a pair of leaves, egg-shaped (hence the second Latin name), near the base, acute, with five marked veins, opposite.
The flowers are green, small, loosely arranged on a very long narrow raceme or spike. The inner petals are narrower, with a lip divided into two nearly to the base. The column has a crest or appendage, on which the anther is placed. The anthers are yellow, the sepals deep-green, and the petals yellow. When touched the rostellum, one of the stigmas, emits a sticky fluid.
The Tway-blade is about 1 ft. high. The flowers bloom in May and June. This orchid is perennial, propagated by division of the root.
The pollen is friable, and if not aggregated into a pollen mass would not adhere. It lies above the rostellum, and when the latter is touched it exudes a clammy fluid which rises to the level of the pollen. All the visitors are Ichneumons except Gram-moptera lcevis. They attach the pollinia or pollen masses to the head, and apply them to fresh stigmas. Alighting on the lower part of the labellum or lip, they creep up, licking the honey in the groove, and raising the head they touch the rostellum, from the side of which fluid exudes. This fluid which rises to the apex of the pollinia cements them to the head of the insect which collects pollinia in each fresh flower. When touched the rostellum bends down to protect the stigma, and while the groove of the labellum is receiving fresh honey it rises, leaving the stigma free for application of new pollinia. The pollinia are erect at first on the insect's head, and then bent down, and they spread apart and so touch the stigma.
The seeds are light, and easily dispersed by the wind.
Tway-blade is a clay-loving plant, common on clay soil in ash-woods and in humus soil.
The leaves of Tway-blade are liable to be attacked by a fungus, Cceoma orchidis.
Photo. Flatters & Garnett - Tway-blade (listera Ovata, Br.)
Listera, R. Brown, is the name by which Dr. Martin Lister (d. 1711) is honoured, and the second Latin name refers to the shape of the leaves.
This orchid is called Bifoil, Double-leaf, Dufoil, Herb Bifoil, Tway-blade, Twifoil.
From its interesting mode of pollination it is worth cultivating, and requires sandy, clayey, or peaty loam.
Essential Specific Characters: 289. Listera ovata, Br. - Stem erect, pubescent, leaves in opposite pairs, ovate, flowers in a lax spike, green, sticky, column crested.