Burmanniaceae
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Gymnosiphon bekensis in Cameroon |
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The Burmanniaceae are a family of plants from the order of the yam-like (Dioscoreales). The family includes around one hundred species in nine genera, which are often monotypical or very poor in species. The ancestral family is widespread worldwide in the tropics, most of its species are completely without leaf green and instead feed on mycoheterotrophs as parasites of fungi. Due to their independence from light as a source of energy, they open up ecological niches that plants otherwise remain largely closed to.
Due to the evolutionary adaptations to their way of life, the leaf-greenless species were attested "a bizarre appearance" and they were compared with "an artificial flora made of glass in which the small flowers in brilliant colors like crystals rest on the delicate, glass-like stems".
description
Appearance
All species of the family are mycotrophic and - except for around forty species of the genus Burmannia - chlorophyllless , annual or perennial herbaceous plants . They usually reach heights of growth of 5 to 30 centimeters, some Burmannia species only up to 2 centimeters, maximum values are 75 or even 100 centimeters ( Burmannia disticha ). Almost all species grow terrestrially , epiphytes are rarely found ( Burmannia kalbreyeri , Burmannia longifolia ).
Rhizome and roots
The tuber-like, cylindrical and usually vertically growing rhizome is branched, only a few centimeters long and densely covered with overlapping scales and thread-like, exogenously grown roots with mycorrhizae . Root hairs are missing, but in the genus Dictyostega they may be functionally replaced by the edges of the rhizome scales or long hairs at their tips. The mykoheterotrophic species lack root caps. The roots have a pronounced endodermis with U-shaped wall thickenings and / or Caspary's stripes . The central cylinder is slightly tri- or tetrarchic and has only one to six xylem vessels with ring or screw-shaped wall reinforcements and three to eight phloem strands . No sieve tube plastids were detected. The pericycle is almost completely reduced.
In the center of the rhizomes there is marrow tissue as well as the vascular bundle cylinder - sometimes surrounded by an endodermis - the bark is thickened compared to the above-ground part of the plant. Both marrow tissue and bark serve as starch stores .
Species of the Burmanniaceae can also reproduce vegetatively by means of shoots growing laterally from the rhizome or axis buds from the root. Two types of Burmannia ( Burmannia alba , Burmannia longifolia ) are known to have root dimorphism . In addition to a rather weak root system, there is also one, sometimes even two very thickened, tuberous roots.
The leaf-green species of the genus Burmannia usually deviate from this structure : they lack the rhizome and they have root caps. With a height of up to 70 centimeters, they are also among the largest members of the family.
Shoot axes
Above-ground shoot axes are only developed in the form of the inflorescence axes , they are usually unbranched and cylindrical in cross-section, around their base there is a sheath about 1 millimeter high starting from the main root . The epidermis has almost no stomata , if so, with no side cells ( anomocytische stomata ). Inwardly, there is a pronounced subepidermal tissue, a sclerenchymal sheath , an endodermis similar to that of the roots. There are 3 to 20 reduced collateral vascular bundles . The xylem vessels have ring and spiral thickenings.
leaves
The alternate , sessile leaves are reduced to small scaly leaves in mycotrophic species and are pale brown, yellow, reddish in color, rarely completely colorless. In leaf-green species they are up to 50 centimeters long, linear to lanceolate and usually form a rosette on the lower part of the stem axis . Stipules are missing. The leaves have only one collateral vascular bundle, which consists of a few tracheids , rarely of vessels. For Burmannia fadouensis and Burmannia pingbianensis the formation of axillary bulbs for the purpose of vegetative reproduction has been reported.
Inflorescences and flowers
In the terminal inflorescences there are single (for example in Apteria ) or double ( Gymnosiphon , Dictyostega ) wraps in which one to fifteen stalked flowers are each over a bract . In the case of double wraps, the flowers are oriented on one side. The inflorescences are rather loose in Gymnosiphon and Dictyostega , compact in Miersiella and some Burmannia . The length of the flower stalks is of great taxonomic importance , especially within the genus Gymnosiphon . The usually radial symmetrical and tubular to trumpet-shaped flowers are threefold. The flower color is variable, often from blue to light blue, but also green, yellow, white or pink. Different colors are often combined with one another in high contrast.
The fully intergrown tepals stand in two circles, the outer three are significantly larger than the inner ones, only with Campylosiphon this difference is hardly pronounced. In Marthella the tepals of the inner circle are completely absent. The tepals of the outer circle are mostly simple, (only three-lobed in the genera Cymbocarpa and Gymnosiphon ); those of the inner circle are greatly reduced, simple (with Hexapterella occasionally three-lobed) and fleshy thickened. In the bud, the flush outer tepals completely enclose the inner tepals. The perianth is persistent, so it is not thrown off until the fruit is ripe, but slowly dries up; Exceptions are Gymnosiphon , Cymbocarpa and Hexapterella gentianoides , which are described as circumscissil, so here all the flower elements above the flower tube are thrown off and leave behind a "bare flower tube".
There is only one circle with three stamens opposite the inner tepals , the outer stamen circle is missing. Stamens are absent with the exception of the genera Apteria and Marthella and Hexapterella gentianoides . The counters tear open across and are clearly separated from each other. The stylus is as long as the flower, triangular to round in cross section at the base, cylindrical above, thread-shaped and at the tip at the level of the anthers in three funnel-shaped or two-lipped stigma branches. With two-lipped scar branches, the lower lip is covered with papillae , which serve as points of attachment for the pollen.
The three pistils have become an under constant ovary grown. The ovary has one or three compartments. In three subjects ( Burmannia ) the placentation is central angled, in one mostly parietal. The ovules are anatropic, bitegmic and tenuinucellate.
Nectaries have been found for numerous members of the family , from simple septal nectaries in Burmannia and Campylosiphon to highly complex glandular structures in Miersiella umbellata and Marthella trinitatis , where six fused glands, each arranged in pairs, are placed above the ovary.
Fragrances are only released weakly, sporadically or for a short time; a uniform picture cannot be drawn. Individual reports are available for Burmannia championii (sweet), Hexapterella gentianoides (sweet), Campylosiphon purpurascens (fragrant), Gymnosiphon divaricatus (pleasant, primrose-like) and another type of Gymnosiphon (after cocoa). The papillae on the inner sides of the perianth are considered to be the source of the scents.
Pollen
The pollen is described as extremely diverse, only very few characteristics apply to the entire family. The pollen grains are mostly scattered as monads , i.e. individually, rarely do they form groups of four ( tetrads ) or two ( dyads ) pollen grains (for example in Apteria aphylla ). In some types of Gymnosiphon , large aggregations are scattered at the same time ( massula ). The surface of the very thin exine is perfectly smooth, the shape of the grain is ellipsoid and its length is between 17 and 54 micrometers . The exine thins out at the apertures and the intine emerges. Most of the pollen is porous (the pores are occasionally eccentric to the equator of the pollen grain), the number of pores is very variable and can vary even within a species. Monoporate and diporate pollen predominate, occasionally there are species with three pores. Rarely found inaperturate ( gymnosiphon , apteria aphylla , Burmannia sphagnoides ), even more rarely monocolpate pollen ( Cymbocarpa refracta , Hexapterella gentianoides ).
Fruits and seeds
The capsule fruits are single or triple, open lengthways (with the exception of several transverse slits in the Burmannia ) and contain many tiny seeds, which in the leaf-green species are spread by wind ( boleochory ), in the mycoheterotrophic species by water ( hydrochory ) .
The seeds are 0.19 to 1.52 millimeters long, 0.06 to 0.55 millimeters wide, rounded-oval to elongated, yellow to brown, shiny and wingless. The funiculus is relatively long, an endosperm is present, but only extremely weak.
genetics
The chromosome numbers range from 6 and 8 through 68 to 87 to 99. The presence of polyploidies is assumed, but an exact basic chromosome number (possibly 6 or 8) is not known.
ecology
pollination
So far, only self-pollination has been observed in Burmanniaceae . It occurs regularly in many species and is facilitated by several adaptations: the anthers and stigmas are brought closer together, the anthers open in the bud, and pollen tubes sometimes grow from the anther to form the stigma. For Apteria aphylla there is a report of visits by mites, which, however, due to their restricted mobility, can only pollinate the plants with their own pollen. In some Burmannia species there is celistogamy , the flower remains closed and self-fertilization occurs ( Burmannia championii , Burmannia lutescens , Burmannia capitata ), in Burmannia coelestis apomixis was also observed, a completely asexual form of reproduction.
However, the adaptations of the flowers of many species indicate cross- pollination . Partly there is protandry (the anthers ripen before the carpels, thus avoiding self-pollination), the flower structure is clearly adapted to the visit by insects, also in the form of the nectar production of many species. Butterflies are assumed to be pollinators due to the structure of the flowers . In the corolla tubes of three specimens of Gymnosiphon breviflorus , which were used as test material, a "Hymenoptere from the relation of the ore wasps [...] was found twice , in the third corolla tube of the same species a fly pupa (or larva) of the suborder Brachycera ".
Way of life
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The majority of all species in the family no longer photosynthesize at all and accordingly do not form chlorophyll . Instead, they live myco-heterotrophically on arbuscular mycorrhizal fungi , so they are completely dependent on the fungi for their nutrition. Since these mycorrhizal fungi are in symbiosis with other plants, mostly trees or shrubs, the term epiparasitism was occasionally used for this constellation . In the strict sense, however, this term is incorrect, since epiparasitism as indirect co-feeding of the fungus partner without damaging the fungus itself does not exist here. Burmanniaceae are real parasites on the fungus: the hyphae of the fungus that grow into the outer up to 12 cell layers of the bark and epidermis of the roots or rhizomes are gradually killed and the nutrients stored in the tissue in the form of starch . Over long periods of time, the subterranean parts of the plant (rhizome, roots) are the only active parts of the plants; they only sprout when they have accumulated sufficient reserves of nutrients from the fungus.
Even though most of the Burmannia species are leaf-green, this does not mean that they have to be autotrophic . They, too, often parasitize fungi, but carry out photosynthesis in parallel; only a few species such as Burmannia disticha are completely free from mycorrhizas. Leake stated in this regard: " It is most likely that many of these species obtain more carbon heterotrophically than they do from photosynthesis [...]") through heterotrophy than through photosynthesis [...] ")
The fungi parasitized by the plants come - as far as known - from the class Glomeromycetes , including not only species from the genus Glomus but also some from the family Acaulosporaceae and Peronosporaceae .
distribution
The Burmanniaceae can be found worldwide in the tropical zones of all continents and rarely reach warm temperate latitudes. Particular focus areas are South America and Asia (Southeast Asia, Malesia ), a smaller focus is West and Central Africa. The family also extends to North America, the Caribbean and Eastern Australia. The distribution between Paleotropic and Neotropic is approximately the same.
The almost worldwide distribution, together with the fact that no species can be found on more than one continent, is a clear indication of the age of the family, which is around 93 million years old for the oldest common representative of the modern species (Crown node age). is specified. The high degree of endemism at the genus level is also particularly noteworthy: While the 14 species in Africa and 39 species in Australasia originate from only three genera ( Burmannia , Gymnosiphon , Saionia ), the 47 New World species are distributed across all 9 genera of the family.
Habitats
The myco-heterotrophic species of Burmanniaceae usually grow on rotting wood or leaves in very shady locations in humid primary forests , but occasionally also in sunny, open locations humus-rich, humus savannahs , in bamboo bushes , pine forests , mangroves or even in moist sand in caves.
The leaf green Burmannia TYPES found in shady, but open, moist to swampy and low humus content sites in savannas, prairies , wetlands , peat moss - bogs , on the banks of ponds and rivers, in gravel pits, cypress swamps and pine forests, as well as rice fields.
Are associated with Burmanniaceae types of grasses , Juncaceae , Cyperaceae , xyridaceae , Eriocaulaceae , Sundew Family , lentibulariaceae , Gentian family , polygalaceae and others in West Africa are characteristic plants of the island mountain -Vegetation. The epiphytic species live in forests on living branches or the stilt roots of palm trees of the genus Iriartea .
The Burmannia TYPES usually grow individually and are found mostly in low altitudes, but can also penetrate to altitudes of up to 3600 meters.
Endangerment and Status
Due to the mostly inaccessible locations, their disjoint distribution area, their inconspicuousness and their natural rarity, no summary statement about the development of the family's population is possible. On the IUCN Red List are three species of the genus Gymnosiphon , four species of the genus Afrothismia , four or five species of the genus Burmannia and one species of the genus Oxygyne . In the USA, Burmannia flava in Florida has been classified as "Endangered" since 1998.
In particular, the status of Marthella trinitatis , the only species in its genus, is unclear ; it was collected only once in 1883 on El Tucuche , the second highest mountain in Trinidad , and has not been found since then, but it does not enjoy official status. The same applies to the Cymbocarpa saccata, which has only been found three times .
Systematics
Genera
The Burmanniaceae currently comprise (including the Thismiaceae ) around 16 genera with around 170 species, but new species (especially the genus Burmannia ) are regularly described. Except for Afrithismia with around 14 species, Gymnosiphon with around 30 species, Burmannia with around 60 species and Thismia with around 64 species, all genera have only one to four representatives.
- Afrothismia Schltr. : This subheading includes about 14 species that occur in Africa. Some authors also place them in the Thismiaceae family.
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Apteria Nutt. : It includes only one type:
- Apteria aphylla (Nutt.) Barnhart ex Small : It occurs in tropical and subtropical America.
- Burmannia L. (Syn .: Tripterella Michx. ): This subheading includes around 60 species.
- Campylosiphon Benth. : There are two types here.
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Cymbocarpa Miers : This subheading includes two species:
- Cymbocarpa refracta Miers : It occurs in tropical America.
- Cymbocarpa saccata Sandwith : Found only three times, in Guiana, Peru and northern Brazil.
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Dictyostega Miers : With only one species, which is divided into three subspecies:
- Dictyostega orobanchoides (Hook.) Miers : It occurs in tropical America.
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Geomitra Becc. : It contains only one type:
- Geomitra clavigera Becc. : It occurs in Thailand, Malaysia, Sumatra and Borneo.
- Gymnosiphon flower : With about 30 species in the tropics.
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Haplothismia Airy Shaw : It contains only one species: It is also placed in the Thismiaceae family by some authors .
- Haplothismia exannulata Airy Shaw : It occurs in southern India.
- Hexapterella Urb. : This subheading includes two species that occur in the Neotropic.
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Marthella Urb. : With only one type:
- Marthella trinitatis (Johow) Urb. : It occurs in northern Trinidad .
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Miersiella Urb. : With only one type:
- Miersiella umbellata (Miers) Urb. : It occurs in tropical South America.
- Oxygyne Schltr. : It contains four species that occur from Cameroon to the Central African Republic. Some authors also place them in the Thismiaceae family.
- Saionia Hatus. : It was set up in 2015. Some authors also place them in the Thismiaceae family. Their three types occur only in southern Japan up to the Nansei Islands .
- Thismia handle. : This subheading includes about 64 species. Some authors also place them in the Thismiaceae family.
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Tiputinia P.E.Berry & CLWoodw. : It has only one species. It was first described in 2007. Some authors also place it in the Thismiaceae family .
- Tiputinia foetida P.E.Berry & CLWoodw. : It occurs in eastern Ecuador.
History of the system
The history of the systematics of the Burmanniaceae is characterized in many respects by uncertainties due to the sometimes extremely reduced morphology of their mykoheterotrophic representatives.
The Burmanniaceae family were established by Blume in 1830 with the three genera Burmannia , Gymnosiphon and Gonyanthes (the latter was later put as a synonym for Burmannia ) after Linné the two Burmannia species he knew, Burmannia disticha and Burmannia biflora, when they were first published in 1753 Order Monogynia (class Hexandria) attributed (families as taxa were not originally used in Linnaeus' system). The generic name Burmannia honors the Dutch botanist and doctor Johannes Burman , a friend of Linnaeus. The holotype is a specimen of Burmannia disticha from Ceylon, today kept in the Swedish Museum of Natural History.
The family was subjected to a first revision by Miers from 1847 to 1851 . At the same time he introduced a further subdivision of the family into two subfamilies, the Thismiae and the Burmanniae, which were represented with partly varying ranks until the turn of the millennium (see for example Maas-van de Kamer 1998).
Hooker and Bentham classified the family in 1883 on the basis of morphological features such as mycotrophy, subordinate ovary, very small seeds and - as with the orchids - an endosperm assumed to be missing together with the orchids in the microsperm order and divided them into three tribes, since they too still incorporated the Corsiaceae into the family. This summary was decisive until the publication of Jonkers monograph in 1938, Engler also took it over, but also included the monotypical genus Geosiris in the family.
The apparent relationship with the orchids can still be found in Cronquist , who incorporated the Burmanniaceae into the Orchidales order. Poor Tachtadschjan, however, placed the Burmanniaceae, just like Robert Folger Thorne , with the Corsiaceae in a separate order Burmanniales.
The couple Hiltje Maas-van de Kamer and Paul JM Maas from the University of Utrecht, Traudel Rübsamen and, more recently, Dianxiang Zhang , Vincent Merckx and Peter Schols made significant contributions to the knowledge of the Jonker family .
Phylogenetics
On the basis of molecular genetic studies, all of the approaches outlined above were increasingly questioned. Neither Thismiae nor Corsiae could be confirmed as part of the Burmanniaceae, to the Corsia as part of the Liliales there is probably not even an indirect relationship. Since the beginning of the 21st century, all tribes have therefore been understood as separate families that are not directly related to one another. The Angiosperm Phylogeny website lists the Burmanniaceae as part of the Dioscoreales , with the Dioscoreaceae as a sister group.
The internal systematics of the previous Burmanniae, which remain the only member of the family, is also in need of revision, according to the investigations. So the Burmannia are paraphyletic . The status of the genus Cymbocarpa is also considered dubious; it may be included in the genus Gymnosiphon .
The currently most extensive and most recent study of the Merckx family gives the relationships in the family as follows (greatly simplified, names in bold represent several taxa):
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The investigations also showed that the loss of chlorophyll occurred several times independently of one another. This is interpreted as an indication that there is generally a basic genetic disposition within the family that allows a switch to a mycotrophic way of life.
use
The Burmanniaceae species are largely insignificant to humans. The species Apteria aphylla and Burmannia biflora , described as astringent and bitter-tasting after isolated samples , were used as tea plants, and Burmannia coelestis was reported to be used as a medicinal herb by the Santals in West Bengal .
literature
Most of the information in this article has been taken from the following sources; for more information, see Individual references:
- Hiltje Maas-van de Kamer: Burmanniaceae. In: Klaus Kubitzki (Ed.): The Families and Genera of Vascular Plants. Volume 3, Berlin 1998, ISBN 3-540-64060-6 .
- Traudel Rübsamen: Morphological, embryological and systematic studies on Burmanniaceae and Corsiaceae (with a view of the Orchidaceae-Apostasioideae). 1986, ISBN 3-443-64004-4 .
- Dianxiang Zhang: Systematics of Burmannia L. (Burmanniaceae) in the Old World . In: Hong Kong University Theses Online, Thesis (Ph. D.). University of Hong Kong, 1999.
- Fredrik Pieter Jonker: A monograph of the Burmanniaceae. In: Meded. Bot. Mus. Herb. Rijks Univ. Utrecht , Volume 51, 1938, pp. 1-279.
- PJM Maas, H. Maas-van de Kamer, J. van Bentham, HCM Snelders, T. Rübsamen: Burmanniaceae . In: Flora Neotropica , Monogr. 42, 1986, pp. 1-189.
Individual evidence
- ↑ Traudel Rübsamen: Morphological, embryological and systematic studies on Burmanniaceae and Corsiaceae (with a view of the Orchidaceae-Apostasioideae) , 1986, p. 9.
- ^ R. Ciferri: L'habitat e la micorrizia di alcune Burmanniacee della Repubblica Dominicana . In: Atti Ist. Bot. "Giovanni Brosi" , Ser. V, 7, pp. 25-34, translation quoted from: Traudel Rübsamen: Morphological, embryological and systematic studies on Burmanniaceae and Corsiaceae (with a view of the Orchidaceae-Apostasioideae) , 1986, p. 9.
- ^ Dianxiang Zhang: Systematics of Burmannia L. (Burmanniaceae) in the Old World. In: Hong Kong University Theses Online, Thesis (Ph.D.), University of Hong Kong, 1999, pp. 16-17.
- ↑ Traudel Rübsamen: Nectaries of the Burmanniaceae (Burmannieae). In: Acta Bot. Neerl. , Volume 32, Issue 4, 1983, p. 351.
- ↑ a b Traudel Rübsamen: Morphological, embryological and systematic studies on Burmanniaceae and Corsiaceae (with a view of the Orchidaceae-Apostasioideae) , 1986, pp. 90-91, plate 75.
- ↑ a b JH Kirkbride Jr., CR Gunn, MJ Dallwitz: Burmanniaceae In: Family Guide for Fruits and Seeds , Version 1.0, 2006, accessed: August 12, 2007, ( at the weblinkarchiv. ( Memento from January 19, 2008 in the Internet Archive ))
- ↑ Traudel Rübsamen: Morphological, embryological and systematic studies on Burmanniaceae and Corsiaceae (with a view of the Orchidaceae-Apostasioideae) , 1986, Table XVII, p. 141.
- ^ Stephan Imhof: Subterranean structures and mycotrophy of the achlorophyllous Dictyostega orobanchoides (Burmanniaceae) . In: Revista de Biología Tropical , Volume 49, No. 1, 2001, online , accessed September 3, 2007
- ↑ Jonathan R. Leake: The Biology of Myco-Heterotrophic ('Saprophytic') Plants. In: New Phytologist , Volume 127, Issue 2, 1994, p. 179.
- ↑ Thassilo Franke, Ludwig Beenken, Matthias Döring, Alexander Kocyan, Reinhard Agerer: Arbuscular mycorrhizal fungi of the Glomus-group A lineage (Glomerales; Glomeromycota) detected in myco-heterotrophic plants from tropical Africa . In: Mycological Progress, 2006, Vol. 5, p. 28
- ↑ Jonathan R. Leake: Plants parasitic on fungi: unearthing the fungi in myco-heterotrophs and debunking the 'saprophytic' plant myth. In: Mycologist Volume 19, 2005, pp. 113-122.
- ↑ Dianxiang Zhang: Systematics of Burmannia L. (Burmanniaceae) in the Old World , in: Hong Kong University Theses Online, Thesis (Ph.D.), University of Hong Kong, 1999, p. 13.
- ↑ T. Janssen, K. Bremer: The age of major monocot groups inferred from 800+ rbcL sequences. In: Bot. J. Linnean Soc. , Volume 146, 2004, pp. 385-398.
- ^ Dianxiang Zhang: Systematics of Burmannia L. (Burmanniaceae) in the Old World . In: Hong Kong University Theses Online, Thesis (Ph.D.), University of Hong Kong, 1999, Table 1–1, p. 30.
- ^ Search for "Burmanniaceae" in the IUCN Red List of Threatened Species .
- ↑ See entry in Atlas of Florida Vascular Plants , Online , accessed September 30, 2007
- ↑ a b c d e f g h i j k l m n o p q r s t u Rafaël Govaerts (ed.): Burmanniaceae. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved June 24, 2018.
- ↑ Hiroyoshi Ohashi: Resurrection of Saionia ( Thismiaceae ). In: Journal of Japanese Botany. Volume 90, Issue 2, 2015, p. 116.
- ↑ Carolus Linnaeus: Species Plantarum , Volume 1, pp. 287, 1753 ( botanicus.org )
- ↑ A picture of the holotype can be found on the website of the Swedish Museum of Natural History
- ↑ Overview of the various placements according to Flowering Plant Gateway : Vascular Plant Family Finder , Online , accessed on September 25, 2007.
- ^ A b Dianxiang Zhang: Phylogenetic reconstruction of Burmannia L. (Burmanniaceae): a preliminary study. In: Acta Phytotaxonomica Sinica , 2001, Volume 39, 3, pp. 203-223.
- ↑ Ray Neyland: A phylogeny inferred from large-subunit (26 S) ribosomal DNA sequences suggests that Burmanniales are polyphyletic. In: Australian Systematic Botany , Volume 15, 2002, pp. 19-28
- ↑ a b V. Merckx, P. Schols, H. Maas-van de Kamer, P. Maas, S. Huysmans, E. Smets: Phylogeny and evolution of Burmanniaceae (Dioscoreales) based on nuclear and mitochondrial data. In: Am. J. Bot. , Volume 93, 2006, pp. 1684-1698.
- ↑ See the cladogram for the Dioscoreales on the Angiosperm Phylogeny website .
- ↑ Traudel Rübsamen: Morphological, embryological and systematic studies on Burmanniaceae and Corsiaceae (with a view of the Orchidaceae-Apostasioideae) , 1986, p. 56.
- ^ Fredrik Pieter Jonker: A monograph of the Burmanniaceae , In: Meded. Bot. Mus. Herb. Rijks Univ. Utrecht , Volume 51, 1938, p. 14.
