Neotropical Stegnospermataceae

Jon L.R. Every

Royal Botanic Gardens, Kew, UK. 

Description

Small, xerophytic trees or shrubs, 1-8 m tall, usually with long, weeping branches, sometimes woody, scrambling vines, completely glabrous, bark grey to reddish brown. Leaves simple, alternate, spirally arranged, petiole short, blade fleshy, margin entire, slightly revolute; exstipulate. Inflorescences axillary cymules (condensed and umbellate) or terminal racemiform thyrses; bracts 1-3 subtending the flowers, bracteoles 2 when present. Flowers hypogynous, hermaphroditic, actinomorphic, sepals (4-)5, in one whorl, free, slightly united at the base, green, persistent; corolla (2-)5, shorter than the sepals, free, greenish/reddish to white (probably of staminodial origin), imbricate, slightly clawed; stamens 5-8(-10), united at the base, in one whorl, free from perianth (the opposite-sepalous members) or adnate (the alternisepalous members basally joined to the corolla), filaments connate at base; anthers dorsifixed, opening by longitudinal slits; ovary superior, carpels 2-5, syncarpous, initially 3-5 locular, becoming unilocular with a central column; style short or absent, stigmas 3-5, free, recurved; one ovule per carpel. Fruit a globose, coriaceous capsule, dehiscing by (3-)-5 valves. Seeds (1-)3-5, covered by a white (red at maturity) aril, testa smooth, thin, endosperm not copious, perisperm copious, embryo curved.

Notes on delimitation

  • Recognised as a distinct monogeneric family due to distinct wood anatomy. 
  • Evidence from floral, palynological, biochemical, anatomical, embryological and molecular characters places it securely in the core Caryophyllales but not closely related to any individual family (Cuenoud et al. 2002). However, it has sometimes been treated as Stegnospermoideae, one of six sub -families of the Phytolaccaceae (Nowicke 1968).

Distribution in the Neotropics

  • A monogeneric family with four species, three of which are found in Northwestern Mexico, just outside the floristic region but considered here. The remaining species (Stegnosperma cubense A.Rich.) can be found in Costa Rica and the Caribbean Islands of Cuba, Dominican Republic and Puerto Rico.
  • Found in dry habitats, from dry forest to semi-desert.
  • In the most arid regions it occurs only on sites that are suggestive of perennial ground water.
  • Found frequently in coastal habitats.
  • Seems to be somewhat salt tolerant.

Distinguishing characters (always present)

  • 3-5 carpellate, unilocular ovary.
  • Carpels alternating with perianth.
  • Capsular, leathery fruit.
  • Arillate seed.
  • Filaments fused at the base, to form a ring.

Other important characters

  • Petals of staminodal origin (shorter than the sepals).
  • Stamens longer than the flower.
  • Black, shiny seed.

Key differences from similar families

Number of genera

  • 1:  Stegnosperma Benth.

Status

Native: Stegnosperma cubense A.Rich.

 

Endemic (outside floristic region): Stegnosperma halimifolium Benth., Stegnosperma sanchezii Medrano & Medina, Stegnosperma watsonii  D. J. Rogers

General notes

  • Stegnosperma from the Greek "Covered Seed ".
  • In contrast to the majority of the Caryophyllales the carpels of Stegnosperma alternate with the inner perianth.

Important literature

Bedell, H.G. 1980.  A Taxonomic and Morphological Re-Evaluation of Stegnospermaceae (Caryophyllales). Systematic Botany 5(4): 419-431.

Brown, G.K. and Varadarajan, G.S. 1985.  Studies in Caryophyllales I: Re-evaluation of Classification of Phytolaccaceae s.1. Systematic Botany 10(1): 49-63.

Cuénoud, P., Savolainen, V., Chatrou, L.W., Powell, M., Grayer, R.J., and Chase, M.W. 2002.  Molecular phylogenetics of Caryophyllales based on nuclear 18S rDNA and plastid rbcL, atpB, and matK DNA sequences. American J. Bot. 89: 132-144.

Culham, A. 2007.  Stegnospermataceae. In: V.H. Heywood, R.K. Brummitt, A. Culham and O. Seberg (eds.). Flowering Plant Families of the World, p. 310. Royal Botanic Gardens, Kew.

Maas, P.J.M. and Westra, L.Y.Th. 2005.  Neotropical Plant Families. 3rd ed. Pp. 132-133. A.R.G. Gantner Verlag K.G., Ruggell.

Nowicke, J.W. 1968.  Palynotaxonomic study of Phytolaccaceae. Annals of the Missouri Botanical Garden 55(3): 294-364.

Rogers, D.J. 1949.  Stegnosperma. A new species and a generic commentary. Annals of the Missouri Botanical Garden 36(4):475-477.

Rohwer, J.G. 1993.  Stegnospermataceae. In: K. Kubitzki, J.G. Rohwer and V. Bittrich (eds.). Families and genera of vascular plants volume 2, pp. 592-3. Springer-Verlag, Berlin.

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

Watson, L. and Dallwitz, M.J. 1992 onwards.  The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000.

How to cite

Every, J.L.R. (2009). Neotropical Stegnospermataceae. In: Milliken, W., Klitgård, 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/Stegnospermataceae.htm.