- Name also: Yellow Lady’s-slipper, Woodpecker Nuksack, Lady’s Slipper Orchid
- Family: Orchid Family – Orchidaceae
(formerly Lady’s Slipper Orchid Family – Cypripediaceae)
- Growing form: Perennial herb. Rootstock horizontal, creeping.
- Height: 20–50 cm (8–20 in.). Stem with glandular hairs.
- Flower: Perianth irregular (zygomorphic), 6–9 cm (2.4–3.6 in.) wide. Tepals 6 in 2 whorls: 5 lanceolate–elliptic, reddish brown–dark brown (sometimes lime green), 2 often fused, 1 elaborated into a labellum. Labellum pouch-like, deeply concave, yellow, spurless. Androecium and gynoecium fused into a column, stamens 2, stigmas 3. Flowers usually solitary, sometimes 2–3. Flower with fruity scent.
- Leaves: Alternate, stalkless. Leaves 3–6, becoming smaller towards crown. Blade widely elliptic–lanceolate, tapered, with entire margins, parallel-veined, underside short-haired.
- Fruit: Ridged, approx. 3 cm long capsule, seeds minute, dust-like.
- Habitat: Broad-leaved forests, fens and rich mixed bogs and swamps, grove-like forest margins, sometimes in dry places too. Calcicolous.
- Flowering time: June.
- Endangerment: Near threatened, protected in all of Finland, including the Åland Islands.
Lady’s slipper is often placed in a family of its own rather than with the other orchids because it lacks the long, specialised pollinia that are typical of orchids. Instead it has a mass of sticky pollen on the end of two stamens. Despite its primitiveness, many people regard lady’s slipper as our finest orchid.
Lady’s slipper is one of Finland’s largest flowers with a diameter up to ten centimetres and it has a pleasant fragrance. The structure of the flower has adapted to its special pollination mechanism. Lady’s slipper doesn’t secrete nectar or any other material that a pollinator can eat. The appearance of the flower attracts many kinds of insects, especially hymenopterans and flies, which are directed towards the yellow labellum. Upon noticing that the flower has no nectar large insects such as bumblebees leave disappointedly the same way they came in via the large gap in the labellum, thus pollinating the plant. The flower is usually pollinated by small burrowing bees which eventually slip or fall inside the sack as they land on the labellum. The edge of the sack is slippy and inclined inwards, so small insects cannot get back out the way that they fell in. The back of the sack has transparent parts however, windows, which direct the insect to crawl in the right direction: into a tight corridor between the two-branched columns and the labellum. By leaving the flower via the corridor the sticky mass of pollen attaches itself to the insect’s back. Despite the hard, unrewarding work bees don’t avoid lady’s slipper’s flowers – which would be unfortunate indeed for the flower. The secret of lady’s slipper’s undeniable attraction is its fragrance, which is partly the same as burrowing bees’ pheromones. Apart from the fact that the flower secretes this itself, the soft hair covering the sack releases the scent of the insect that is trying to leave. Lady’s slipper has locally adapted to the pollinators in its different habitats, which can be seen from e.g. the length of the labellum, and there are also seemingly differences in its fragrance.