Neotropical Pterostemonaceae

Jon L.R. Every

Royal Botanic Gardens, Kew, UK.  

Description

Shrubs, much branched, to 4 m tall. Leaves crowded at ends of branches, alternate, spiraling, simple, shortly petiolate, lamina elliptical to almost circular, margins finely glandular (hydathodes), dentate/serrate, coriaceous, glossy adaxially, abaxially pubescent with simple, conical or peltate hairs, venation pinnate, pocket domatia present in angles of lateral veins with midrib; stipules small, deciduous. Inflorescence (sub)terminal, few-flowered cymes or corymbs. Flowers actinomorphic, showy, bisexual, epigynous, 5-merous; calyx tubular, 5 triangular lobes, valvate, erect, pubescent, adnate to ovary, persistent; petals free, imbricate, reflexed, pubescent, clawed, persistent; stamens 5, filaments broad, dentate below  apex, opposite sepals; filaments broad, toothed near apex, anthers dorsifixed, dehiscing longitudinally; staminodes 5 lacking anthers, narrower than stamens, alternating with stamens and opposite petals; ovary inferior, 2-5 carpels, syncarpous, 5-locular, ovules 4-6 per locule; style 1, stigmas 5, radiating from centre, short. Fruit a septicidal woody capsule, 5 valved, crowned by persistent sepals and petals. Seeds few, elongate, with cartilaginous testa, reduced at either end.

Notes on delimitation

  • Placed in the Saxifragales as sister to the non-Neotropical Iteaceae (APG2, 2003).
  • Formerly associated with the Escalloniaceae and Hydrangeaceae.
  • Included in the Grossulariaceae by Cronquist (1981).

Distribution in the Neotropics

  • Central and Southern Mexico.
  • Arid hilly regions.
  • Particularly prevalent on limestone and chalk, elevation 1400-2650 m.

Distinguishing characters (always present)

Other important characters

  • Pocket domatia present.
  • Water glands present (hydathodes).
  • Stipules (falling).
  • Scented flowers, white to pink.

Key differences from similar families

The following families may be confused with Pterostemonaceae, but differ in the characters listed below:

Escalloniaceae:

Grossulariaceae:

Hydrangeaceae:

  • Leaves opposite.

Iteaceae:

Rosaceae:

Number of genera

  • One genus: Pterostemon S. Schauer  2 spp. (P. mexicanus S. Schauer; P. rotundiflourus Ramírez).

Status

  • Endemic.

General notes

  • Glandular hairs secrete resin which gives the top of the leaf a glossy finish.

Important literature

APG II, 2003. An update of the Angiosperm Phylogeny group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141(4): 399-436.

Berkov, A. 2004.  Pterostemonaceae. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds). Flowering Plants of the Neotropics. p.316. The New York Botanical Garden, Princeton University Press Princeton.

Cronquist, A. 1981. An Integrated System of Classification of Flowering Plants. Columbia University Press, New York.

Kubitzki, K. 2007. Pterostemonaceae in Families and genera of vascular plants. Volume 9. Flowering plants. Eudicots.Pp. 405-6. Springer-Verlag Berlin, Heidelberg, New York.

Maas, P.J.M. & Westra, L.Y. Th. 2005.  Neotropical Plant Families. 3rd ed, p.149. A.R.G. Gantner Verlag K.G., Ruggell.

Perez-Caliz, E. 2003. Pterostemonaceae. Flora del Bajio y de regions adyacentes. Fasciculo 116. Patzcuaro, Michoacan : Instituto de Ecologia.

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

Watson, L.& Dallwitz, M.J. (1992 onwards).  The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version 3rd March 2009. http://delta-intkey.com