Hederorkis Thouars, Nouv. Bull. Sci. Soc. Philom. Paris 19: 319 (1809).
Heterotypic Synonyms:
Scandederis Thouars, Hist. Orchid.: t. 91 (1822), nom. inval.

An epiphytic or lithophytic, robust plant. Stem scandent, sympodial rhizo-matous, covered with imbricate sheaths disintegrated into fibres, pseudobulbs rudimentary,. Leaves two, arising from the top of each shoot, elliptic, acute, divergent, thick, shortly articulated to a sheath. Inflorescence lateral simple raceme arising from a node on rhizome or near tip of shoot, few-flowered, longer than leaves. Flowers non-resupinate. Sepals and lateral petals free, somewhat similar, elliptic to oblanceolate, obtuse. No mentum. Lip ecallose, free to base, sparsely hairy on upper surface, obscurely trilobed, the lateral lobes erect, upcurved at the tips, the middle lobe porrect, larger than the lateral ones. Gynostemium elongate, slender, gently arched; column part free, much longer than the anther, narrowly winged, column foot rudimentary; anther incumbent, operculate, subglobose, slightly dorsiventrally compressed; connective narrow, rather thin; pollinia 4, in two pairs, obliquely superposed, unequal in size and form, oblong-ellipsoid, hard, caudiculae sticky, connecting pollinia with tegula; apical clinandrium obscure, collar-like; stigma elliptic, deeply concave; rostellum bent forwards, short, truncate; viscidium single, oblong-obovate, lamellar, delicate; tegula single, oblong, lamellar; rostellum deeply incised after removal of pollinarium.
Its name is derived from two words, Latin hedera (ivy) and Greek orkis (orchid) and refers to the scandent habit of the plant.
Hederorkis scandens Thouars.
Taxonomic note:
Hederorkis, described in 1809 by du Petit Thouars has been considered to belong to Bulbophyllum (note in Kew Herbarium, according to Cribb in and Hunt. However, Bosser indicated closer relationship of the genus to Polystachya due to the gynostemium structure, and Dressler agreed. Thouars used two set of names in his revolutionary system Rasmussen clarified the nomenclature of H. scandens.
Both species of Hederorkis are plants with similar habit and floral structure; however, Hederorkis seychellensis is a larger, more robust plant with an oblong, fleshy lip adorned by two longitudinal calli in the basal third. The lip of Hederorkis scandens is smaller, deeply constricted in the middle, widest in apical half and free from any callosities. Hederorkis seychellensis is uncommon in Mahé and very rare in Silhouette and probably does not occur in Aldabra. The material collected in Aldabra atoll is sterile and may not represent this species. H. scandens is known from four localities in Mauritius and one from Réunion. The islands on which the species occur are small and well known botanically, but Hederorkis have been reported from very few localities. The range of distribution of both species of Hederorkis coincide with an area of extremely high floral diversity and endemism, the Madagascar and the Indian Ocean Islands hotspot. The hotspot is one of the world’s top conservation priority due to its remarkable biodiversity and extensive deforestation. A potential distribution range for both species is relatively small, the known extent of occurrence of Hederorkis seychellensis is about 170 km2 and about 4560 km2 of Hederorkisscandens. Moreover, the islands are residential and strongly deforested, so the extent of potential habitats for Heredorkis is quite limited.
A key to the species of Hederorkis
The two species have different ecological requirements, which is associated with different weather conditions. The Mascarenes, where H. scandens occurs, are sometimes subjected to very high levels of rainfall, up to 6,000 millimeters per year in La Réunion, in contrast, the Seychelles, where Hederorkis seychellensis grows, are relatively dry region with a lower altitude reaching only 914 millimeters at its highest in Mourne Seychellois National Park, however the climate in La Réunion can be dry on western slopes.
W. Indian Ocean.
Bibliography and References:
BosserJ (1976) Le genre Hederorkis Thouars (Orchidaceae) aux Mascareignes et aux Seychelles. Adansonia II 16(2): 225-228.
Burns-Balogh P, Funk VA (1986) A phylogenetic analysis of the Orchidaceae. Smithsonian Contr Bot 61:1-79.
Carnevali G, Cetzal-Ix W, Balam R, Leopardi C, Romero-Gonzalez GA (2013) A combined evidence phylogenetic re-circumscription and a taxonomic revision of Lophiarella (Orchidaceae: Oncidiinae) SystBot 38(1): 46-63.
Chase MW, Cameron KM, Barrett RL, Freudenstein JV (2003) DNA data and Orchidaceae systematics: a new phylogenetic classification. In: Dixon KM, Kell SP, Barrett RL, Cribb PJ, editors. Orchid conservation. Malaysia: Natural History Publications. pp. 69-89.
Chase MW, Hills HH (1991) Silicagel: an ideal material for field preservation of leaf samples for DNA studies. Taxon 40:215-220.
Cribb PJ (2014) Subtribe Polystachyinae, Taxonomic notes. In: Pridgeon AM, Cribb PJ, Chase MW, Rasmussen FN. Genera Orchidacearum, Volume 6: Epidendroideae (Part 3). Oxford University Press. 544 p.
Cuénoud P, Savolainen V, Chatrou LW, Powell M, Grayer RJ, Chase MW (2002) Molecular phylogenetics of Caryophyllales based on nuclear 18S rDNA and plastid rbcL, atpB, and matK DNA sequences. Am J Bot 89:132-144.
Douzery EJP, Pridgeon AM, Kores P, Linder HP, Kurzweil H, Chase MW (1999) Molecular phylogenetics of Diseae (Orchidaceae): a contribution from nuclear ribosomal ITS sequences. Amer J Bot 86: 887-899. PMID: 10371730
Dressler RL (1981) The orchids: natural history and classification. Cambridge, Massachutes, Harvard University Press. 394 p.
Dressler RL (1990) The orchids: natural history and classification. Harvard University Press, U.S.A. 332 p.
Dressler RL (1993) Phylogeny and classification of the orchid family. Dioscorides, USA. 312 p.
Felsenstein J (1985) Confidence limits on phylogenies: an approach using the bootstrap. Evolution 39: 783-791.
Fitch WM (1971) Toward defining the course of evolution: minimal change for a specific tree topology. SystZool 20:406-416.
Freudenstein JV, BergC, Goldman DH, Kores PJ, Molvray M, Chase MW (2004) An expanded plastid DNA phylogeny of Orchidaceae and analysis of Jackknife branch support strategy. Amer J Bot 91: 149-157.
Gautier N, Gouy M, Gautier C (1996) SeaViewand Phylo_win, two graphic tools for sequence alignment and molecular phylogeny. Comput Applic Biosci 12: 543-548.
Gerlach J (1997) Seychelles Red Data Book 1997. NPTS, Seychelles.
GorniakM, Paun O, Chase MW (2010) Phylogenetic relationships within Orchidaceae based on a low-copy nuclear coding gene, Xdh: Congruence with organellarand nuclear ribosomal DNA results. Mol Phylogen Evol 56(2): 784-95.
Hunt PF (1968) African orchids: XXXII. Kew Bull 22:489-492.
Molvray M, Kores PJ, Chase MW (2000) Polyphyly of mycoheterotrophic orchids and functional influences on floral and molecular characters. In: Wilson KL, Morrison DA, editors. Monocots: Systematics and Evolution. Australia: CSIRO Publishing, Collingwood, Victoria. pp. 441-448.
Mytnik-Ejsmont J, Szlachetko DL (2011) Chelystachya, a new genus of the subtribe Polystachyinae (Orchidaceae). Biodiv Res Conserv 23:17-29.
Pridgeon AM, Bateman RM, Cox AV, Hapeman JR, Chase MW (1997) Phylogenetics of subtribe Orchi-dinae (Orchidoideae, Orchidaceae) based on nuclear ITS sequences. 1. Intergeneric relationships and polyphyly of Orchis sensu lato. Lindleyana 12: 89-109.
Rasmussen F (1979) Nomenclatural notes on Thouars' works on orchids. Bot Not 132: 385-392.
Robertson SA (1989) Flowering Plants of Seychelles. Royal Botanic Gardens, Kew, Richmond. 327 p.
Schlechter R (1926) Das System derOrchidaceen. NotizblBotGartMusBerlin-Dahlem 9(88): 563-591.
Senghas K (1990-1991) 56. Subtribus: Cymbidiinae. In: Brieger FG, Maatsch R, and Senghas K. Schlechter R.-Die Orchideen 3rd ed. Paul Parey, Berlin.
Shaw J, Lickey EB, Beck JT, Farmer SB, Liu W, Miller J etal. (2005) The tortoise and the hare II: relative utility of 21 noncoding chloroplast DNA sequences for phylogenetic analysis. Am J Bot 92: 142-166.
Shaw J, Lickey EB, Schilling EE, Small RL (2007) Comparison of whole chloroplast genome sequences to choose noncoding regions for phylogenetic studies in angiosperms: The tortoise and the hare III. Am J Bot 94: 275-288.
Sun Y, Skinner DZ, Liang GH, Hulbert SH (1994) Phylogenetic analysis of Sorghum and related taxa using internal transcribed spacers of nuclear ribosomal.
Swofford DL (2002) PAUP. Phylogenetic Analysis Using Parsimony (and other methods), version 4.0 Beta. Sunderland, Massachusetts: Sinauer Associates.
Szlachetko DL(1995) SystemaOrchidalium. Fragm FlorGeobot 3:1-152.
Thiers B. (continuously updated). Index Herbariorum: A global directory of public herbaria and associated staff. New York Botanical Garden's Virtual Herbarium.
Thompson JD, Gibson TJ, Plewniak F, Jeanmougin F, Higgins DG (1997) The ClustalX windows interface: flexible strategies for multiple sequence alignment aided by quality analysis tools. Nucleic Acids Research 24:4876-4882.
Thouars A du Petit (1809) Extrait de trois mémoires. Nouveau Bulletin des Sciences, Publié par la Société Philomathique 1:314-319.
Thouars A du Petit (1822) Histoire particulière des plantes orchidées recueillies dans les trois îles australes de France, de Bourbon et de Madagascar. Paris.
Whitten WM, Williams NH, Chase MW (2000) Subtribal and generic relationships of Maxillarieae (Orchidaceae) with emphasis on Stanhopeinae: combined molecular evidence. Amer J Bot 87:1842-1856.
Wise RA (1998) A fragile Eden: Portraits of the endemic flowering plants of the granitic Seychelles. Princeton: Princeton University Press. 216 p.