Phalaenopsis (), also known as moth orchids, is a genus of about seventy species of plants in the family Orchidaceae. Orchids in this genus are monopodial epiphytes or lithophytes with long, coarse roots, short, leafy stems and long-lasting, flat flowers arranged in a flowering stem that often branches near the end. Orchids in this genus are native to Asia, New Guinea, and Australia, but mostly occur in Indonesia and the Philippines.
Description
Orchids in the genus Phalaenopsis are monopodial epiphytic, sometimes lithophytic herbs with long, coarse roots with pneumatodes (which allow for gaseous exchange of the photosynthetic roots), and short leafy stems hidden by overlapping leaf bases. The leaves are usually arranged in two rows, relatively large and leathery, oblong to elliptic and sometimes succulent. A few to many, small to large, long-lasting, flat, often fragrant flowers are arranged on erect to hanging racemes or panicles. The sepals and petals are free from and spread widely apart from each other. The lateral sepals are usually larger than the dorsal sepal and the petals much wider than the sepals. The labellum is joined stiffly to the column and has three lobes. The side lobes are erect and more or less parallel to each other and the middle lobe sometimes has a pair of appendages or antennae.
Reproduction Unlike most other angiosperms, the development of the ovules is triggered by pollination. Therefore a temporal mismatch of male and female gametes exists (i.e. the male structures are ready but the female structures have not yet been fully developed). In orchids, fertilisation occurs within days or months after the pollination event. After pollination occurs, the stigmatic cavity is often closed through swelling of the column. As a result, the pollinia are completely enclosed. The pollen germinates after enclosure and tubes are produced. In Phalaenopsis aphrodite, pollen tubes entered the ovary within 3 days after pollination. Within 15 days, pollen tubes evenly spread throughout the placental cavities. Within 60 days after the pollination event, 30.6% of the tips of the pollen tubes started to enter the micropyles (i.e. entry points) of the ovules. Finally, 65 to 70 days after the pollination event, fertilisation occurred. Phalaenopsis are unique in that in some species of the subgenus Polychilos, the flowers turn into green leaves after pollination. As in many other plants, the petals of the orchid flowers serve to attract pollinating insects and protect essential organs. Following pollination, petals usually will undergo senescence (i.e. wilt and disintegrate) because it is metabolically expensive to maintain them. However, in many Phalaenopsis species, such as P. violacea, the petals and sepals find new uses following pollination, thus escaping programmed cell death. In producing chloroplasts, they turn green, become fleshy, and start to photosynthesize, as leaves do.
Phytochemistry Floral fragrance has been analysed for several species. The fragrance of Phalaenopsis bellina has been shown to be composed of about 79 compounds, primarily of the terpenoid class. It was most intense in the morning. In Phalaenopsis, phenylpropanoid enzymes are enhanced in the process of plant acclimatisation at different levels of photosynthetic photon flux.
Taxonomy The genus Phalaenopsis was first formally described in 1825 by Carl Ludwig Blume and the description was published in Bijdragen tot de flora van Nederlandsch Indië. The name Phalaenopsis is derived from the Ancient Greek word φαλαινα (phalaina) meaning 'a kind of moth' with the suffix -opsis meaning 'having the appearance of' or 'like'. The genus name is abbreviated Phal. horticulturally.
Infrageneric structure The large monophyletic genus Phalaenopsis is divided into several sub-units. They are either regarded as subgenera or as sections. Not all of them are monophyletic. The subgenus Polychilos is monophyletic and it is divided into two subclades. The subgenus Phalaenopsis is paraphyletic under its current definition. Likewise the evidence shows that the subgenera Aphyllae and Parishianae, as currently defined, are not monophyletic. The position of the monotypic subgenus Proboscidioides, which only consists of Phalaenopsis lowii, suggests a close relationship with the subgenus Aphyllae. The following phylogenetic tree is a simplified tree to show the general placement of the main infrageneric groups. It is meant to give an overview, despite the contended monophyly of some of the respective groups.
Ornithochilus
The former genus Ornithochilus was merged with Phalaenopsis and is considered by some to be a subgenus. Its members have distinctly 4-lobed, fringed labella with a short, curved spur situated near the middle of the lip as opposed to the base. Ornithochilus formerly had three known species, native to China, the Himalayas and Southeast Asia:
Ornithochilus cacharensis Barbhuiya, B.K.Dutta & Schuit. - Assam Ornithochilus difformis (Wall. ex Lindl.) Schltr. - Guangdong, Guangxi, Sichuan, Yunnan, Assam, India, Bhutan, Nepal, Myanmar, Thailand, Vietnam, Laos, Borneo, Sumatra, Peninsular Malaysia Ornithochilus yingjiangensis Z.H.Tsi - Yunnan
Hygrochilus
The former genera Sedirea and Hygrochilus were incorporated into Phalaenopsis subgen. Hygrochilus. The interspecific relationships within the subgenus Hygrochilus are poorly understood and are a source of confusion. The type species of the subgenus is Phalaenopsis hygrochila. The species of this subgenus are morphologically distinct from the other subgenera, due to their four pollinia and spurred flowers, as well as their unusually long stems.
Species list See List of Phalaenopsis species
Intergeneric hybrids See List of Phalaenopsis species
Distribution Species of Phalaenopsis are found from India to southern China, Indochina, Malaysia and from Indonesia to the Philippines and New Guinea. There is a single species, Phalaenopsis rosenstromii, endemic to Queensland, Australia. Phalaenopsis stuartiana has become naturalised in Costa Rica, Panama, and Suriname.
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