Neotropical Picrodendraceae

Hans-Joachim Esser

Botanische Staatssammlung München, Munich, Germany. 

Description

Trees or rarely shrubs, deciduous or not, lacking latex and extrafloral nectaries. Leaves alternate (rarely opposite), 3-(5-)foliolate, 1-foliolate or rarely simple, margins entire to (rarely) spinose-dentate, petiole present, short to long, eglandular, stipules present but caducous, rarely intrapetiolar and covering the terminal bud, eglandular, scaly to large; indumentum simple; venation pinnate, veinlets densely reticulate (rarely percurrent). Inflorescences unisexual, dioecious, axillary or (rarely) epiphyllous and partially adnate to petiole, fasciculate-glomerulate or in elongate raceme -like or cymose inflorescences or (pistillate) flowers sometimes solitary; bracts small, inconspicuous. Flowers actinomorphic, pedicellate, with imbricate, free to nearly free sepals, petals absent. Staminate flowers with (3-)4-9 sepals, 4-19(-54) stamens, filaments free, anthers dorsifixed to basifixed, extrorse to introrse, bilocular, opening with longitudinal slits, disc present or rarely absent, intrastaminal, flat and often covering receptacle, pollen 4-8-zonoporate, with short colpi, tectate, exine spinulose, pistillode minute or absent. Pistillate flowers with 4-9 sepals, staminodes present or absent, disc annular and variously lobed (rarely absent), ovary hypogynous, syncarpous, with (2-)3 locules, glabrous to pubescent, ovules 2 per locule, placentation axile, anatropous, bitegmic, style usually distinct, rarely short to absent, stigmas (2-)3, short or linear, entire or rarely bilobed. Fruits septicidally dehiscent schizocarps with 3(-6) seeds or (rarely) indehiscent drupaceous, usually 1-seeded by abortion (sometimes 2-seeded). Seeds ellipsoid to ovoid, smooth, anatropous, ecarunculate, without sarcotesta, endosperm copious (rarely absent), embryo straight, cotyledons broad, rarely ruminate. Chromosome number 2n = 48 (Picrodendron), but unknown for most genera.

Notes on delimitation

  • The Picrodendraceae were included in the Euphorbiaceae as part of the subfamily Phyllanthoideae or as a separate subfamily Oldfieldioideae for a long time, but are distinguished by, for example unusual pollen and mostly compound leaves.
  • Separate family status was also confirmed by molecular phylogenies.
  • Many genera are mono- or ditypic, and most are endemics, e.g., in Australia, New Caledonia or Madagascar. Paradrypetes (opposite leaves, epiphyllous inflorescences) and Picrodendron (embryos with ruminate cotyledons, bitter taste of bark etc.) are very unusual by the cited characters, but seem to be part of the Picrodendraceae, supported by the characteristic pollen.
  • Podocalyx is still insufficiently known. Therefore the exact circumscription of the family is not completely settled.

Distribution in the Neotropics

The Picrodendraceae are represented by five genera in the Neotropics, all endemic with quite restricted distribution, occurring in several lowland vegetation types including humid evergreen forests, dry deciduous forests or arid scrubland:

  • Paradrypetes Kuhlm.: 2 spp., endemic to Brazil (SW Amazonia and Atlantic Coastal Forest).
  • Parodiodendron Hunz.: 1 sp. [P. marginivillosum (Speg.) Hunz.], in drier forests of Bolivia and NW Argentina.
  • Piranhea Baill.: 4 spp., from Mexico to the Brazilian Amazon.
  • Picrodendron Planch.: 1 sp. [P. baccatum (L.) Krug & Urb. ex Urb.], restricted to the Caribbean islands except for Puerto Rico.
  • Podocalyx Klotzsch: 1 sp. [P. loranthoides Klotzsch], restricted to Northern Amazonia (Colombia, Venezuela, Brazil).

Distinguishing characters (always present)

  • Dioecious woody plants.
  • Small unisexual apetalous flowers.
  • Ovaries with two anatropous ovules per carpel, fruits however with one ecarunculate seed per carpel by abortion (2-seeded carpels very exceptional).
  • Pollen with 4-8 zonal pores and distinctly spinulose exose.

Other important characters

  • Leaves 3-foliolate or 1-foliolate.
  • Flowers often with an irregular number of sepals.
  • Fruits subglobose septicidal schizocarps or drupes.

Number of genera

Picrodendraceae are pantropical and comprise c. 25 genera and 80 species. In the Neotropics they are represented by 5 genera:

  • Paradrypetes Kuhlm.
  • Parodiodendron Hunz.
  • Picrodendron Planch.
  • Piranhea Baill.
  • Podocalyx Klotzsch

Notable genera and distinguishing features

  • Paradrypetes - leaves opposite and spinose-dentate, with intrapetiolar stipules, fruits usually 1-seeded drupe.
  • Parodiodendron - leaves 1-foliolate, a pair of lateral leaflets reduced to stipellae on the upper leaf base, leaf margin ciliate.
  • Picrodendron - leaves 3-foliolate, fruits 2-seeded drupes, seeds with ruminate cotyledons.
  • Piranhea - leaves 3-(5-) foliolate, fruits 3-seeded schizocarps.

Status

  • Native and endemic.

Important literature

Govaerts, R., Frodin, D.G. & Radcliffe-Smith, A. 2000. World checklist and bibliography of Euphorbiaceae (with Pandaceae). London: Royal Botanic Gardens, Kew.

Hayden, W.J., Gillis, W.T., Stone, D.E., Broome, C.R. & Webster, G.L. 1984. Systematics and palynology of Picrodendron: further evidence for relationship with the Oldfieldioideae (Euphorbiaceae). J. Arnold Arbor. 65: 105-127.

Hunziker, A. 1969. Parodiodendron gen. nov.: un nuevo genero de Euphorbiaceae (Oldfieldioideae ) de Noroeste Argentino. Kurtziana 5: 331-341.

Levin, G.A. 1992. Systematics of Paradrypetes (Euphorbiaceae). Syst. Bot. 17: 74-83.

Radcliffe-Smith & J.A. Ratter. 1996. A new Piranhea from Brazil, and the subsumption of the genus Celaenodendron (Euphorbiaceae: Oldfieldioideae). Kew Bull. 51: 543-548.

Wurdack K.J., Hoffmann, P., Samuel, R., de Bruijn, A., van der Bank, M. & Chase, M.W. 2004. Molecular phylogenetic analysis of Phyllanthaceae (Phyllanthoideae pro parte, Euphorbiaceae sensu lato) using plastid rbcL DNA sequences. Amer. J. Bot. 91: 1882-1900.

How to cite

Esser, H.-J. (2010). Neotropical Picrodendraceae. 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/Picrodendraceae.htm.