Hoya (plant)
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Hoya | |
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Hoya bella | |
Scientific classification | |
Kingdom: | |
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Order: | |
Family: | |
Genus: | Hoya |
Species | |
See text. | |
Synonyms | |
Madangia |
Hoya is a genus of 200-300 species of tropical plants in the family Apocynaceae (Dogbane family), formerly considered to be in the Asclepiadaceae (milkweed family). Most are native to Asia including India, China, Thailand, Malaysia, and Indonesia, There is a great diversity of species in the Philippines, and species in Polynesia, New Guinea, and Australia.
Common names for this genus are waxplant, waxvine, waxflower or simply hoya. This genus was named by botanist Robert Brown, in honour of his friend, botanist Thomas Hoy.
Summary
Hoyas are evergreen perennial creepers or vines or rarely, shrubs. They often grow epiphytically on trees; some grow terrestrially, or occasionally in rocky areas. They climb by twining, and with the employment of adventitious roots. Larger species grow 1–18 m (3–59 ft), or more, with suitable support in trees. They have simple entire leaves, arranged in an opposite pattern, that are typically succulent. Leaves may exhibit a variety of forms, and may be smooth, felted or hairy; veination may be prominent or not, and many species have leaf surfaces flecked with irregular small silvery spots.
The flowers appear in axillary umbellate clusters at the tip of a peduncles. Hoya peduncles are commonly referred to as spurs. In most species these spurs are perennial and are rarely shed. Each flowering cycle increases the length of the spur, and in the larger species can eventually reach 27 cm (11 in) or more. Flowers vary in size from 3 mm (0.1 in) (Hoya bilobata Schltr.) to over 95 mm (4 in) (in H. lauterbachii K. Schuman) in diameter. Flower form is typically star-shaped, with five thick, waxy, triangular petals, topped with another star-shaped structure, the corona. Colours on most species range from white to pink; there are species that exhibit yellow to orange, dark reds to near-black, and there are green flowers. Many are sweetly scented. and most produce abundant nectar.
Pollinators include moths, flies, and ants. Pollination is poorly understood, but plants left outdoors in temperate regions do sometimes produce seed, indicating pollination by local insects.
Seeds are borne in twin pods, actually follicles, are generally light, and are dispersed by the wind by means of a small tuft of silky fluff. Germination is rapid, but viability is not long.
At least some species exhibit Crassulacean Acid Metabolism (CAM), including H. carnosa.
Several species exhibit adaptations for mutualism with ants by providing modified leaves for domatia ("homes"), much as in the related genus Dischidia; H. imbricata has leaves that form a concave cup over the tree trunk it climbs up to shelter ants, and H. darwinii has arrangements of bullate leaves on its stems to form shelters.
Cultivation and uses
Many species of Hoya are popular houseplants in temperate areas (especially H. carnosa), grown for their attractive foliage and strongly scented flowers. Numerous cultivars have been selected for different leaf forms or flower colours. Hoyas grow well indoors, preferring bright light, but will tolerate fairly low light levels, although they may not flower without bright light. Hoyas commonly sold in nurseries as houseplants include cultivars of H. carnosa (Krimson Queen, Hindu Rope − compacta), H. pubicalyx (often mislabelled as H. carnosa or H. purpurea-fusca), and H. kerrii. Hoyas are easy to propagate, and are commonly sold as cuttings, either rooted or unrooted, or as a potted plant.
Hoya carnosa has been shown in recent studies at the University of Georgia to be an excellent remover of pollutants in the indoor environment.
Various cultures have used Hoyas medicinally, especially Polynesian cultures. Some are toxic to livestock and sheep poisonings in Australia are reported.
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Hoya carnosa
as a houseplant -
Hoya carnosa
Inflorescence peduncle, several years old -
Hoya carnosa
Inflorescence -
Hoya carnosa
Single flower -
Hoya obovata
Ant feeding on nectar. Flowers are very fragile.
Leaves
Hoya leaves vary in size, texture, color and venation. In size, leaves range from as small as 5 mm in length and 2 to 4 mm in width (Hoya engleriana Hosseus) to as large as 25 cm by 35 cm. (Hoya latifolia G. Don). Hoya coriacea Blume, has been reported have leaves as long as two feet in length. There are hoyas with almost perfectly round leaves and others with linear leaves (Hoya linearis Wall. ex. D. Don and Hoya teretifolia Griff. ex Hook. f.). One popular species, Hoya shepherdii Short ex Hook. has leaves that resemble string beans hanging in bunches from their stalks. Hoya linearis Wall. ex D. Don is covered with fine downy hair and resembles masses of Spanish Moss (Tillandsia useneoides) hanging from trees in its native habitat. Some Hoya leaves are smooth and shiny; some are covered with hairs. Some Hoya leaves appear to be veinless while others have very conspicuous veins of a lighter or darker colour than the rest of the leaves as in H. cinnomomifolia. Some have leaves that are mottled with speckles of silvery white (Hoya carnosa R. Br., Hoya pubicalyx). Some hoyas have leaves that are thin and translucent (Hoya coriacea Blume); some are so thick and succulent that they look more like crassulas than hoyas (Hoya australis ssp. rupicola, oramicola and saniae from Australia and Hoya pachyclada from Thailand). One of the most succulent, Hoya kerrii Craib, has valentine heart shaped leaves, with notches at the apexes of the leaves instead of at the bases.
Flowers
Hoya flowers are all shaped like five pointed stars. Some of the species' petals reflex so far that the flowers appear to be round or ball-like. They grow in umbels, or in some species singly. Umbels can reach impressive proportions in some species, and many species have individual flowers well over three inches in diameter (H. imperialis Lindl., H. lauterbachii K. Schuman). H. coriacea Blume has been known to have as many as 70 in an inflorescence, each individual measuring nearly 2 cm in diameter with the umbels over 30 cm in breadth. The single-flowered Hoya pauciflora Wight makes up for its paucity by its flower size of nearly an inch and a half in diameter produced at any time of year. Textures of flower surfaces may be glabrous and shiny, to matte, to finely haired, and some being quite hairy. One of the two clones of Hoya mindorensis Schltr., from the Philippines, comes very close to being a true red. Blue, purples, and violets do not appear to be represented in the genus Hoya.
Selected species
- Hoya acicularis
- Hoya acuminata
- Hoya acuta
- Hoya aeschynanthoides
- Hoya affinis
- Hoya africana
- Hoya alagensis (Philippines)
- Hoya alata
- Hoya alba
- Hoya albens
- Hoya albiflora
- Hoya aldrichii (Christmas Island)
- Hoya alexicaca
- Hoya amboinensis
- Hoya ambon
- Hoya amoena
- Hoya andalensis
- Hoya angustifolia (Philippines)
- Hoya angustisepala
- Hoya anncajanoae (Philippines)
- Hoya anulata
- Hoya apiculata
- Hoya apoda
- Hoya archboldiana
- Hoya ariadna
- Hoya arnottiana
- Hoya attenuata
- Hoya augustifolia
- Hoya aurantiaca (Philippines)
- Hoya australis - Australian Waxflower (Australia, Papua New Guinea)
- Hoya australis ssp. australis
- Hoya australis ssp. keysii
- Hoya australis ssp. naumanii
- Hoya australis ssp. oramicola
- Hoya australis ssp. rupicola
- Hoya australis ssp. sana
- Hoya australis ssp. tenuipes
- Hoya bandensis
- Hoya bella - Beautiful Hoya
- Hoya benguetensis (Philippines)
- Hoya benitotanii (Philippines)
- Hoya benvergarai (Philippines)
- Hoya betchei
- Hoya bhutanica
- Hoya bicknellii (Philippines)
- Hoya bilobata (Philippines)
- Hoya blashernaezii (Philippines)
- Hoya bordenii (Philippines)
- Hoya brevialata
- Hoya buotii (Philippines)
- Hoya burtoniae (Philippines)
- Hoya cagayanensis (Philippines)
- Hoya callistophylla
- Hoya calycina
- Hoya calycina ssp. calycina
- Hoya campanulata
- Hoya camphorifolia (Philippines)
- Hoya cardiophylla - Heart Leaf Hoya (Philippines)
- Hoya carnosa - Porcelain Flower, Waxplant (China, Souheast Asia, Malesia)
- Hoya caudata
- Hoya cembra - syn. Hoya odorata
- Hoya chlorantha
- Hoya chuniana
- Hoya chunii
- Hoya ciliata - syn. Eriostemma ciliata (Philippines)
- Hoya cinnamomifolia
- Hoya citrina
- Hoya clandestina
- Hoya clemensii
- Hoya clemensiorum
- Hoya collina
- Hoya cominsii
- Hoya compacta
- Hoya conchoi
- Hoya coriacea - syn. Hoya angustisepala (Philippines)
- Hoya coronaria
- Hoya crassicaulis (Philippines)
- Hoya crassipes
- Hoya cumingiana (Philippines)
- Hoya curtisii (Philippines and Thailand)
- Hoya cystiantha
- Hoya dasyantha
- Hoya darwinii - Ant Hoya (Philippines)
- Hoya davidcummingii (Philippines)
- Hoya dennisii
- Hoya densifolia (Philippines)
- Hoya deykei
- Hoya dickasoniana
- Hoya dimorpha
- Hoya diptera
- Hoya dischorensis
- Hoya diversifolia (Thailand, Malaysia, Indonesia, Philippines)
- Hoya dolicosparte
- Hoya edenii
- Hoya eitapensis
- Hoya elliptica (Thailand, Malaysia, Philippines)
- Hoya endauensis
- Hoya engleriana
- Hoya erythrina
- Hoya erythrostemma (Thailand)
- Hoya eitapensis
- Hoya excavata
- Hoya filiformis
- Hoya finlaysonii
- Hoya fischeriana (Philippines)
- Hoya fitchii (Philippines)
- Hoya flagelleta
- Hoya flavescens
- Hoya flavida
- Hoya fraterna
- Hoya fungi
- Hoya fusca
- Hoya fuscomarginata
- Hoya gigantangensis - syn. Hoya benitotanii (Philippines)
- Hoya gigas
- Hoya gildingii
- Hoya glabra
- Hoya globulosa
- Hoya golamcoiana (Philippines)
- Hoya gonoloboides
- Hoya gracilis - invalid name, syn. Hoya memoria (Philippines)
- Hoya graveolens
- Hoya greenii (Philippines)
- Hoya grifithii
- Hoya guppyi
- Hoya halconensis (Philippines)
- Hoya halophila
- Hoya hasselti
- Hoya heuschkeliana (Philippines)
- Hoya heuschkeliana ssp. cajanoae (Philippines)
- Hoya heuschkeliana ssp. heuschkeliana (Philippines)
- Hoya hellwigiana
- Hoya hypolasia (Papua New Guinea)
- Hoya imbricata - syn. Hoya pseudomaxima (Indonesia, Philippines)
- Hoya imperialis (Philippines, Malaysia)
- Hoya imperialis ssp. rauchii (Malaysia)
- Hoya inconspicua
- Hoya incrassata (Philippines)
- Hoya incurvula
- Hoya ischnopus
- Hoya javanica - syn. Hoya multiflora (Malaysia)
- Hoya juanngoiana (Philippines)
- Hoya kanyakumariana
- Hoya kastbergii
- Hoya kenejiana
- Hoya kentiana (Philippines)
- Hoya kerrii - Heart Hoya (Philippines, Thailand)
- Hoya kloppenburgii (Malaysia)
- Hoya krohniana (Philippines)
- Hoya kuhlii
- Hoya lacunosa
- Hoya lacunosa ssp. lacunosa
- Hoya lacunosa ssp. pallidiflora
- Hoya lambii
- Hoya lamingtoniae
- Hoya landgrantensis (Philippines)
- Hoya lasiantha
- Hoya latifolia
- Hoya lauterbachii
- Hoya lazaroi (Philippines)
- Hoya leytensis (Philippines)
- Hoya limoniaca
- Hoya linavergariae (Philippines)
- Hoya linearis
- Hoya litoralis
- Hoya lobbii
- Hoya loherii (Philippines)
- Hoya longifolia
- Hoya lucardenasiana (Philippines)
- Hoya lucyae (Philippines)
- Hoya macgillivrayi
- Hoya macgregorii (Philippines)
- Hoya macrophylla
- Hoya madulidii - syn. Eriostemma madulidii (Philippines)
- Hoya magnifica
- Hoya megalaster
- Hoya meliflua (Philippines)
- Hoya meliflua ssp. fraterna (Philippines)
- Hoya meliflua ssp. meliflua (Philippines)
- Hoya membranifolia
- Hoya memoria (Philippines)
- Hoya meredithii
- Hoya merrillii (Philippines)
- Hoya micrantha
- Hoya microphylla
- Hoya microstemma
- Hoya minahassae
- Hoya mindorensis (Philippines)
- Hoya minibelle
- Hoya mitrata (Malaysia)
- Hoya monetteae (Philippines)
- Hoya montana
- Hoya motoskei - Spotted Waxplant
- Hoya multiflora - Shooting Star Hoya (Malesia)
- Hoya myrmecopa (Indonesia, Philippines)
- Hoya naumanii
- Hoya nabawanensis
- Hoya neo-caledonica
- Hoya neo-ebudica
- Hoya nicholsoniae
- Hoya nummularioides
- Hoya nyhuusiae
- Hoya oblongata
- Hoya obovata
- Hoya obscura (Philippines)
- Hoya obtusifolia
- Hoya obtusifolioides
- Hoya odetteae (Philippines)
- Hoya odorata (Philippines)
- Hoya onychoides
- Hoya oreogena
- Hoya ovalifolia
- Hoya pachyclada
- Hoya padangensis
- Hoya palawanica' (Philippines)
- Hoya pallilimba
- Hoya panayensis (Philippines)
- Hoya panchoi (Philippines)
- Hoya pandurata
- Hoya parasitica
- Hoya parviflora
- Hoya patella
- Hoya pauciflora
- Hoya paxtoni
- Hoya paziae (Philippines)
- Hoya pentaphlebia (Philippines)
- Hoya picta
- Hoya pimenteliana (Philippines)
- Hoya platycaulis (Philippines)
- Hoya plicata
- Hoya polystachya
- Hoya polyneura - Fishtail Hoya
- Hoya pottsii
- Hoya praetorii
- Hoya pseudo-littoralis
- Hoya pubera
- Hoya pubicalyx (Philippines)
- Hoya pulchella
- Hoya purpurea
- Hoya purpureo-fusca
- Hoya pusilla
- Hoya querinoensis
- Hoya quinquenervia (Philippines)
- Hoya quisumbingii (Philippines)
- Hoya ramosi
- Hoya retusa
- Hoya revoluta
- Hoya ridleyi
- Hoya rigida
- Hoya rotundifolia
- Hoya ruscifolia - syn. Dischidia ruscifolia
- Hoya salweenica
- Hoya samoensis
- Hoya schneei
- Hoya scortechinii
- Hoya serpens
- Hoya shephardell
- Hoya shepherdii - String Bean Hoya
- Hoya shortechinii
- Hoya siamica
- Hoya siariae (Philippines)
- Hoya sigillatis
- Hoya sipitangensis
- Hoya solaniflora
- Hoya soligamiana (Philippines)
- Hoya spartioides
- Hoya stoneiana
- Hoya subcalva
- Hoya subglabra
- Hoya subquintuplinervis
- Hoya surigaoensis (Philippines)
- Hoya sussuela
- Hoya telosmoides
- Hoya teretifolia
- Hoya thailandica
- Hoya thomsonii
- Hoya tomataensis
- Hoya tsangii (Philippines)
- Hoya uncinata
- Hoya vaccinioides
- Hoya vanuatuensis
- Hoya verticillata (Philippines)
- Hoya viracensis
- Hoya vitchii
- Hoya vitellina
- Hoya vitellinoides
- Hoya vitiensis
- Hoya wallichii
- Hoya walliniana
- Hoya wayetii (Philippines)
- Hoya waymaniae
- Hoya weebella
- Hoya whistleri
- Hoya wibergiae (Philippines)
- Hoya wightii
References
- Kloppenburg, Dale; Wayman, Ann (1992), The Hoya Handbook : a guide for the grower & collector, Medford, OR: Orca Publishing, ISBN 978-0-9630489-1-2
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- Kloppenburg, Dale; Wayman, Ann (1999), The World of Hoyas : a book of pictures (1st ed.), Fresno, Calif.: Hill-n-Dale
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- Kloppenburg, Dale; Wayman, Ann (2005), The World of Hoyas : a book of pictures (revised ed.), Central Point, OR: Orca Publishing, ISBN 978-0-9630489-4-3
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- Endress, Mary E.; Bruyns, Peter V. (2000), "A revised classification of the Apocynaceae s.l.", The Botanical Review, 66 (1): 1–56, doi:10.1007/BF02857781
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- Yang, Dong Sik; Pennisi, Svoboda V.; Son, Ki-Cheol; Kays, Stanley J. (2009), "Screening Indoor Plants for Volatile Organic Pollutant Removal Efficiency", HortScience, 44 (5): 1377–1381, retrieved 2011-11-30
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- Christopher, J.T.; Holtum, J.A.M. (1996), "Patterns of Carbon Partitioning in Leaves of Crassulacean Acid Metabolism Species during Deacidification", Plant Physiology, 112 (1): 393–399, doi:10.1104/pp.112.1.393
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- Zachos, Ellen (1997), "Practical Uses of Various Hoya Species"
External links
- UGA research shows some plants can remove indoor pollutants December 2, 2009