Neotropical Thurniaceae

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

National Herbarium of the Netherlands (Wageningen branch), Wageningen, the Netherlands.

Description

Herbs, perennial, rhizomatous, growing in or near water.  Leaves alternate, tristichous, simple, basal, parallel-veined, V-shaped in transverse section, linear, sheathing basally, the margins often serrateInflorescences globose, terminal heads subtended by several leafy bracts, on long, 3- to 4-angled peduncles.  Flowers bisexual, actinomorphic, sessile, small; tepals 6, free, chaffy, subequal; stamens 6, much exceeding the tepals, anthers longitudinally dehiscent, dithecal, basifixed, introrse; ovary superior, 3-locular, style 1, very short, stigmas 3, elongate, placentation axile, ovules 1-few per loculeFruits 3-angled, loculicidal capsules.  Seeds 1 per locule, fusiform, pointed at both ends.

Notes on delimitation

  • The Thurniaceae are placed in the order Poales in the APG III system (Stevens, 2008; APG III, 2009).
  • In Cronquist (1981) and Takhtajan (2009) we find the family in the Juncales, closely related to Juncaceae.

Distribution in the Neotropics

  • The family consists of two genera with one ocurring in the Neotropics
  • Thurnia Hook.f. (3 spp.) the Guianas and adjacent Amazon region, often on sandy soils in or near water.

     

Distinguishing characters (always present)

  • Large herbs mostly growing in or near water.
  • Leaves basal, linear, often sharply teethed.
  • Inflorescences globose, terminal heads subtended by several leafy bracts.
  • Flowers small, chaffy; seeds fusiform, pointed at both ends.

Key differences from similar families

Thurniaceae can be easily confused with Juncaceae and Cyperaceae.  For the key differences:

1.  Perianth present; fruit a capsule . 2
1.  Perianth mostly lacking or if present consisting of hairs, scales or bristles; fruit a nutlet . Cyperaceae.
2.  Inflorescence a dense and large globose head on a long peduncle; leaf margins serrate; plants of the lowlands of the Guianas and adjacent Amazon region . Thurniaceae
2.  Inflorescence differently shaped; leaf margins never serrate; plants of mountainous areas in the Neotropics . Juncaceae

Number of genera

  • The family consists of two genera with one ocurring in the Neotropics.

    Status

    • Thurnia is native in the Neotropics and is not cultivated.

    Important literature

    A.P.G. III. 2009. An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Bot. J. Linnean Soc. 161: 105-121.

    Cronquist, A. 1981. An integrated system of classification of flowering plants. Columbia University Press. New York

    Kubitzki, K. 1998. Thurniaceae. In: Kubitzki, K. (ed.). The families and genera of vascular plants, vol. 4. Flowering Plants -Monocotyledons. Alismatanae and Commelinanae (except Gramineae), pp. 455-457. Springer Verlag, Berlin, etc.

    Maas, P.J.M. & Westra, L.Y.Th. 2005. Neotropical Plant Families. A concise guide of vascular plants in the Neotropics. 3rd ed., p. 88. A.R.G. Gantner Verlag K.G., Ruggell.

    Stevens, P.F. 2008. Angiosperm Phylogeny Website. Version 9 onwards. http://www.mobot.org/MOBOT/research/APweb/.

    Stevenson, D.W. 2004. Thurniaceae. In: Smith, N.P., Mori, S.A., Henderson, A., Stevenson, D.W., and Heald, S.V. (eds.). Flowering plants of the Neotropics. pp. 486-487. Princeton University Press, Oxford and Princeton.

    Takhtajan, A. 1997. Flowering Plants. Second edition. Springer Verlag, Berlin.