Neotropical Triuridaceae

Paul J.M. Maas and Hiltje Maas-van de Kamer

National Herbarium, Wageningen University Branch, the Netherlands. 

Description

Myco-heterotrophic ("saprophytic"), small herbs, lacking chlorophyll; rhizome mostly well-developed, creeping, provided with many scale-like leaves; roots filiform, very rarely coral-shaped, with or without root -hairs. Stems mostly unbranched, white, yellow, purple, or red. Leaves alternate, sessile, simple, entire, small and scale-like. Inflorescence a terminal, bracteate, few- to many-flowered raceme. Flowers unisexual (then plants monoecious or dioecious) or bisexual, actinomorphic, white, yellow, purplish, or red; tepals 3-6, basally connate, often soon reflexed, inner side often densely papillate, apex sometimes provided with dense tufts of hairs (bearded) or long-tailed; bisexual flowers: 2-6 free stamens and many free ovaries; staminate flowers: 2-6 mostly epitepalous stamens (except for Triuris Miers), free or implanted on a central androphore; anthers dithecic or rarely monothecic (Triuridopsis H.Maas & Maas), 2-4-locular, longitudinally or transversely extrorsely dehiscent; pistillate flowers: 10-many free carpels, implanted on the receptacle; ovary 1-locular with 1 basal, anatropous ovule, apical part of ovary often papillate; style 1, lateral, rarely terminal (Triuris), about as long as the ovary or far exceeding it, stigmatic zone papillate, penicillate, or glabrous. Fruit consisting of achenes or 1-seeded follicles. Seed 1, globose to obovoid, small.

Notes on delimitation

  • Most recent research places this family in the order of Pandanales (Maas & Weustenfeld, 1998, p. 487).
  • The genus Lacandonia E.Martínez & Ramos was previously recognised in a family of its own - Lacandoniaceae.

Distribution in the Neotropics

Family: from Guatemala in the North to S Brazil and N Paraguay in the South, absent in the West Indian Islands.

Genera:

  • Lacandonia E.Martínez & Ramos - Mexico (Chiapas).
  • Peltophyllum Gardn. - SE Brazil and adjacent Argentina and Paraguay, and Guyana.
  • Sciaphila Blume - From Guatemala in the North to S Brazil and N Paraguay in the South.  
  • Soridium Miers - From Guatemala in the North to Brazil (Mato Grosso) in the South.
  • Triuridopsis - Peru (Loreto).
  • Triuris - From Guatemala in the North to S Brazil and N Paraguay in the South.

Distinguishing characters (always present)

Other important characters

  • Flowers often unisexual.
  • Inner side of tepals often densely papillate.
  • Apex sometimes provided with dense tufts of hairs (bearded) or long-tailed.
  • Stamens free or on a central androphore.

Key differences from similar families

  • From the other 2 myco-heterotrophic monocotyledonous families Burmanniacae and Thismiaceae Triuridaceae can be easily distinguished by its flowers which have many free carpels.

Number of genera

6 genera:

  • Lacandonia (1 sp.)
  • Peltophyllum (2 spp.)
  • Sciaphila (8 spp.)  
  • Soridium (1 sp.)
  • Triuridopsis (1 sp.)
  • Triuris (3 spp.)

Useful tips for generic identification

Key to genera of Neotropical Triuridaceae

1. Flowers bisexual; stamens placed in the center of the flower within the carpels ... Lacandonia
1. Flowers unisexual or rarely bisexual, but than the stamens always placed outside and around the carpels ... 2

2. Plants monoecious; flowers unisexual (2 species of Sciaphila bisexual); number of tepals 4, 6, or 8; number of stamens 2, 3, 4, or 6; tepals bearded; style basal; fruit dehiscent or indehiscent... 3
2. Plants dioecious; flowers unisexual; number of tepals 3 or 6; number of stamens 3 or 6; tepals long-tailed; style apical; fruit indehiscent... 4 

3. Staminate flowers with 2 stamens and 4 tepals; fruit an indehiscent achene... Soridium
3. (Staminate) flowers with 3 or 6 stamens, and 4 or 6 tepals; fruit a dehiscent follicle... Sciaphila

4. Staminate flowers with anthers sessile on a conical androphore... Triuris
4. Staminate flowers without conical androphore... 5 

5. Staminate flowers with 3 tepals, 6 filamented, monothecal anthers and a sterile projection in the centre of the flower... Triuridopsis 
5. Staminate flowers with 6 tepals, 3 sessile, dithecal anthers and no sterile projection in the centre of the flower... Peltophyllum                                                                                                                                  

Notable genera and distinguishing features

  • Lacandonia is made unique in the Plant Kingdom by its stamens which are placed in the centre of the flower, surrounded by the apocarpous carpels.
  • One of the species of Sciaphila, S. purpurea Benth., can reach a height of almost 1.5 m! It is often found growing on termites' nests.
  • Triuris is quite spectacular in having 3 long-tailed tepals and in having male flowers with sessile stamens implanted in a fleshy and conical androphore.

Status

  • All genera are native.

General notes

  • Most myco-heterotrophic plant groups in the Neotropics (incl. Burmanniaceae and Thismiaceae) are poorly known and much additional field work needs to be conducted. Peltophyllum caudatum (Poulsen) R.Schmid & M.D.Turner and Triuridopsis peruviana H.Maas & Maas are both only known from 1 collection!
  • Rudall (2003) suggest that flowers of Triuridaceae may equally be interpreted as pseudanthia, i.e. modified and highly reduced partial inflorescences.

Important literature

Maas, P.J.M. and T. Rübsamen. 1986. Triuridaceae. Flora Neotropica Monograph 40: 1-55.

Maas-van de Kamer, H. & P.J.M. Maas. 1994. Triuridopsis,  a new monotypic genus in Triuridaceae. Pl. Syst. Evol. 192: 257-262.

Maas-van de Kamer, H. & T. Weustenfeld. 1998. Triuridaceae. In: K. K. Kubitzki  (ed.), The families and genera of vascular plants 3: 452-458.

Martínez, E. & C.H. Ramos. 1989. Lacandoniaceae (Triuridales): Una nueva familia de Mexico. Ann. Missouri Bot. Gard. 76: 128-135.

Rudall, P.J. 2003. Monocot pseudanthia revisited: Floral structure of the mycoheterotrophic family Triuridaceae. Int. J. Pl. Sci. 164 (5 Suppl.): S307-S320.

How to cite

Maas, P.J.M. & Maas-van de Kamer, H. (2009). Neotropical Triuridaceae. In: Milliken, W., Klitgĺrd, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Triuridaceae.htm.