Neotropical Combretaceae

Maria Iracema Bezerra Loiola

Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil. 

Description

Trees or shrubs often scandent (Combretum Loefl.), mesophytic, xerophytic or halophytic (Laguncularia C.F.Gaertn.), with long, straight, sharply-pointed, unicellular trichomes with very thick walls and with a conical internal compartment at the base (Combretaceous hairs), and with or without stalked glands or glandular scales. Stipules absent. Leaves opposite, alternate, rarely whorled, simple, petiolate, venation pinnate, margins entire. Inflorescences spicate, racemose or paniculate, sometimes globular clusters (Conocarpus L.), terminal or axillary. Flowers usually small, actinomorphic or zygomorphic, bisexual, sometimes unisexual (plants monoecious or polygamous, and rarely dioecious in Conocarpus), 4-5 merous, with hypanthium divided into two regions, a lower surrounding the ovary and an upper narrowed into a shorter or longer tube finished in calyx lobes; bracteoles absent or when present adnate to the hypanthium; calyx lobes usually 4 or 5, connate, sometimes inconspicuous, imbricate to valvate; petals usually 4-5 or absent, small, alternisepalous, imbricate to valvate; androecium usually with 8-10 stamens, commonly in 2 whorls alternating with and opposite the corolla members; filaments long-exserted (Combretum) or included; anthers dorsifixed, versatile or adnate to the filaments (Buchenavia Eichler), dehiscing longitudinally; gynoecium syncarpous, ovary inferior semi-inferior (Strephonema Hook.f.), unilocular, with apical placentation, 2-6 ovules pendulous, non-arillate, anatropous, with long funicle; style simple, usually filiform, free or partially adnate to the upper part of hypanthium, stigma minute, punctate or capitate; nectary usually an intrastaminal disk at the base of hypanthium, disk sometimes absent. Fruits usually indehiscent, rarely dehiscent (in introduced Quisqualis indica Blanco), drupaceous, samararoid or rarely a capsule, often 2-5-winged or -ridged or -angled, with pericarp lignified or not lignified, fleshy (Buchenavia) or dry. Seed 1, non-endospermic; embryo with convolute or plicate cotyledons and small radicle.

Notes on delimitation

  • Combretaceae was traditionally placed in the order Myrtales and analyses based on molecular characters identifies it as the sister clade to the rest of the order.
  • Morphology and rbcL sequence characters both support the monophyly of Combretaceae.

Distribution in the Neotropics

  • Buchenavia Eichler - Mesoamerica, Caribbean, South America.
  • Combretum Loefl - Mexico, Mesoamerica, Caribbean, South America.
  • Conocarpus L. - Mexico, Mesoamerica, Peru, Ecuador, Brazil.
  • Laguncularia Gaertn - Mexico, Mesoamerica, Caribbean, Colombia, Peru, Ecuador, Brazil.
  • Quisqualis L. - (Q. indica introduced from Africa and cultivated).
  • Terminalia L. - Mexico, Mesoamerica, South America.

Distinguishing characters (always present)

  • Leaves simple, entire, petiolate.
  • Ovary inferior.
  • Hypanthium divided into two regions (a lower surrounding the ovary and an upper narrowed into a shorter or longer tube finished in calyx lobes).
  • Trichomes long, straight, sharply-pointed, unicellular, with very thick walls and with a conical internal compartment at the base.

Other important characters

Key differences from similar families

Number of genera

6 genera:

  • Buchenavia
  • Combretum
  • Conocarpus
  • Laguncularia
  • Quisqualis 
  • Terminalia

Useful tips for generic identification

Key to genera of Neotropical Combretaceae

1. Flowers conspicuous; petals more than 10 mm; stamens included in calyx tube ... Quisqualis
1. Flowers small; petals less than 10 mm; stamens exserted or included in calyx tube ... 2

2. Inflorescences globular clusters ; fruit aggregated ... Conocarpus
2. Inflorescence spicate, racemose or paniculate; fruit not aggregated ... 3

3. Lowers receptacle with 2 adnate bracteoles ... Laguncularia
3. Lowers receptacle without adnate bracteoles ... 4

4. Anthers adnate to the filaments ... Buchenavia
4. Anthers versatile ... 5

5. Leaves opposite; trees or shrubs often scandent ... Combretum
5. Leaves alternate or verticillate; trees ...Terminalia

Notable genera and distinguishing features

Combretum:

  • Leaves opposite.
  • Petals 4 or absent.
  • Stamens 4 or 8.
  • Fruit 4-winged.

Terminalia:

Status

  • Buchenavia (native).
  • Combretum (native, cultivated).
  • Conocarpus (native).
  • Laguncularia (native).
  • Terminalia (native, cultivated).
  • Quisqualis (introduced and cultivated).

General notes

  • The family stands out economically for its ornamental value, with some species commercialized by florists worldwide.
  • Others are cited in the literature as having pharmacological potential and being widely used as popular diuretics or antipyretics. A number of species exhibit antimicrobial, antihemorrhagic and antiulcer activities.
  • Conocarpus erectus L. and Laguncularia racemosa (L.) Gaertn. are typical of mangrove areas and are ecologically essential to the dynamics of this ecosystem and to the survival of its organisms. 
  • Laguncularia racemosa shows several adaptations to daily flooding by salt water: the leaves contain salt excretory glands, the seeds germinate while still attached to the tree (vivipary), and the roots include pneumatophores.

Important literature

Brummitt, R. K. 1992. Vascular plants families and genera. Royal Botanic Gardens, Kew. 733pp.

Conti, E.,  Litt, A., Wilson, P. G., Graham, S. A., Briggs, B. G.,  Johnson, L. A. S. & Sytsma, K. J. 1997. Interfamilial Relationships in Myrtales: Molecular Phylogeny and Patterns of Morphological Evolution. Systematic Botany 22 (4): 629-647.

Exell, A. W. & Stace, C. A. 1966. Revision of the Combretaceae. Boletim da la Sociedad Broteriana. sér.2, 40: 5-25.

Loiola, M. I. B. & Sales, M. F. de. 1996. Estudos taxonômicos do gênero Combretum Loefl. (Combretaceae R. Br.) em Pernambuco - Brasil. Arquivos do Jardim Botânico do Rio de Janeiro 34(2): 174-188.

Marquete, N. F. da S. & Valente, M. C. 2005. Flora da Reserva Ducke, Amazonas, Brasil: Combretaceae. Rodriguésia 56 (86): 131-140. 2005.

Stace, C. A. 1980. The significance of the leaf epidermis in the taxonomy of the Combretaceae: conclusions. Botanical Journal of the Linnean Society. London 81: 327-339.

Stace, C. A. Combretaceae. 2007. In: G. Harling & C. Person (eds.), Flora of Ecuador 81: 1-63.

Sytsma, K.J., A. Litt, M.L. Zjhra, J.C. Pires, M. Nepokroeff, E. Conti, Jay Walker, and P.G. Wilson. 2004. Clades, clocks, and continents: historical and biogeographical analysis of Myrtaceae, Vochysiaceae, and relatives in the southern hemisphere. International Journal of Plant Sciences 165 (4 Suppl.): 85-105.

Tan, F., Shi, S., Zhong, Y., Gong, X. & Wang, Y. 2002. Phylogenetic relationships of Combretoideae (Combretaceae) inferred from plastid, nuclear gene and spacer sequences. Journal of Plant Research 15(6): 475-481.

How to cite

Loiola, M.I.B. (2009). Neotropical Combretaceae. 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/Combretaceae.htm.