Caladenia

Caladenia, commonly known as spider orchids, is a genus of 350 species of plants in the orchid family, Orchidaceae. Spider orchids are terrestrial herbs with a single hairy leaf and a hairy stem. The labellum is fringed or toothed in most species and there are small projections called calli on the labellum. The flowers have adaptations to attract particular species of insects for pollination. The genus is divided into three groups on the basis of flower shape, broadly, spider orchids, zebra orchids and cowslip orchids, although other common names are often used. Although they occur in other countries, most are Australian and 136 species occur in Western Australia, making it the most species-rich orchid genus in that state. Orchids in the genus Caladenia are terrestrial, perennial, deciduous, sympodial herbs with a few inconspicuous, fine roots and a tuber partly surrounded by a fibrous sheath. The tuber produces two 'droppers' which become daughter tubers in the following year. There is a single hairy convolute leaf at the base of the plant. Most species have an enlarged cell at the base of each hair. The leaf may be medium-sized to large, fleshy or leathery, lance-shaped to oblong, but is always simple, lacking lobes and serrations. The inflorescence is a raceme with from one to eight resupinate flowers. The three sepals and two petals are free and similar in size and shape to each other. In some species, the sepals or petals or both have narrow tips with club-like ends. As is usual in orchids, one petal is highly modified as the central labellum. The labellum is divided into three parts, each of which usually has a fringed or dentate margin, while the central lobe has stalked or button-like calli which are often in rows. The sexual parts of the flower are fused to the column, which has wing-like structures on its sides. Most species flower in early spring but some species, such as the winter spider orchid (C. drummondii) flower in other months. The fruit that follows flowering is a non-fleshy, dehiscent capsule containing up to 500 seeds. The first specimens of the genus were collected by Joseph Banks in Sydney in 1777 and by Archibald Menzies in King George Sound in Western Australia in 1784. James Edward Smith formally described Arethusa catenata, now known as Caladenia catenata in 1805, from specimens collected in Sydney. The genus was first formally described by Robert Brown in 1810 in Prodromus Florae Novae Hollandiae. At the same time he described 15 species of Caladenia but did not nominate a type species. Brown collected the specimens as a member of Matthew Flinders' mapping and exploration voyage that circumnavigated Australia. He spent just over three years on botanical research with assistants in Australia. The genus name (Caladenia) is derived from the Ancient Greek words kalos meaning 'beautiful' and aden meaning 'a gland' referring to the colourful labellum. There has been disagreement between taxonomists as to which orchids belong in the genus Caladenia and which do not, and about classification within the genus. Recent studies of the molecular phylogenetics of the group suggest that John Lindley’s 1840 description of Caladenia (in The Genera and Species of Orchidaceous Plants), but including Glossodia and Elythranthera, as being the most accurate reflection of the subtribe Caladeniinae. Those orchids previously included in the genera Glossodia, Elythranthera and Cyanicula have been transferred to Caladenia. Caladenia orchids are informally grouped into those with long narrow sepals and petals, such as the white spider orchid (C. longicauda) and the clubbed spider orchid (C. longiclavata), those with short sepals and petals which tend to hang near the stem, such as the zebra orchid (C. cairnsiana) and dwarf zebra orchid (C. pachychila) and a third group with short, spreading sepals and petals such as the cowslip orchid (C. flava) and fan orchid (C. nana).