Tubers usually fusiformly elongated, sometimes slightly thickened at the root. Leaves 2, sometimes only 1 or more, on the shoot or at its base. The inflorescence is several to multi-flowered. Small or medium-sized flowers, turned by 180 °. A sitting ovary. Lingual to lanceolate lip, not patched, at the base with a thread-like or baggy spur of various lengths. The remaining petals are more or less tucked up or both side outer petals widely spread. Stamen straight, connector of different width. Rostellum narrow, shelf-shaped, squeezed between the stamen sacks. Hooks 2, naked. 2-patch mark, narrow, in the shape of a flattened V letter.
Representatives of this genus grow in the Northern Hemisphere, in temperate and tropical zones. It is difficult to determine the number of knee-length species – their systematics is still very confusing. For example, North American researchers include nearly all naked-tipped orchids in this genus, narrow rostel, with a lip provided with a spur, so tongues (Coeloglossum), doves (Leucorchis) or species of the genus Habenaria. A number of minor ones have been described from tropical countries, closely related types to knee-lengths, often defining them ambiguously. Therefore, they are also often combined with knee-lengths. Therefore, it is understandable, there is almost as much of the concept of the type of knee-length, how many researchers working on this group.
It is known in Europe 4(5) species. Najpospolitszymi, also growing in Poland, are the knee socks white (Platanthera bifolia) and a greenish knee (P. chlorantha).
Podkilany grow in various types of forests – from tropical to taiga, besides, in the meadows, peat bogs and in the tundra.
The flowers of both our species are very similar to each other, yes in terms of shape, colors, and size. Both species grow in similar plant communities and bloom at about the same time. Despite this, hybrids between both species are rare. As shown by biochemical studies, both types differ essentially in the nature of the odors they emit. The flowers of the white backbone give off aromatic esters, which lure nocturnal butterflies of the Sphangidae family, while the green knee produces elderberry alcohol, a compound attractive to noctuidae butterflies. It does happen though, that twilight and night butterflies visit the flowers of both species. So why are interspecies hybrids so rare?? The reason is the different structure of the generative parts of both orchids. The connector of the stamen in the white knee is very narrow, as a result, both pollen bags lie close to each other and are parallel. The birthmark in this species is small and is located just above the narrow entrance to the spur. In the greenish knee, the connector is wide, clearly separates both sacks and reveals a large surface of the birthmark. Because the bags are widely spaced, the Rostelmum is also much broader here than in the previous species. The different structure of the rod entails a different way of attaching hobbies and pollinia to the insect's body.. At the knee of the white moth, it is only able to insert the proboscis between the anthers, and in the greenish knee – even the head. The pollinate handles of the first species are very short, they dry quickly on the trumpet, bending forward. So the pollinia sticks to the trumpets here. This allows them to be placed on a narrow birthmark. The handles of the other knee are long and also quickly change their position from vertical to horizontal. However, they are not placed close to each other, stick to the eyes. So they can easily be deposited on a wide and large birthmark.
The nectar in the greenish knee is deeper in the spur than in the white one. So it is available to moths with a suitably long proboscis. These are usually larger insects than the white pollinators. Usually, the distance between their eyes is also greater than the width of the white stamen, therefore the pollen grains cannot be transferred to the stigma of this species. Conversely, the reverse is possible. And this is the most likely way to create hybrids.
Hybrids produce both aromatic esters, as well as elderberry alcohol, so they can attract butterflies of both groups. However, they bear little fruit, because their pollinia easily fall off the bodies of insects.
Pollination of the greenish knee can be quite risky for moths. It happens, that after visiting a few or a dozen flowers, the insect's eyes are mostly stuck with caps, which can significantly lower his chances of survival. Hooks, despite its delicate structure, they stick to insects permanently.
Other species of the genus of knee-lengths are pollinated by daytime butterflies or even mosquitoes.