Combretaceae

Primary tabs

Combretaceae

Description

Trees, shrubs or lianes, sometimes mangroves, not spiny. Leaves opposite (or whorled) or spiral (often ‘alternate’), petiolate, simple, entire, without stipules, often with a pair of petiolar glands. Indumentum almost always of unicellular, slender, thick-walled, pointed hairs with a distinctive basal compartment (‘combretaceous hairs’) alone or with glandular hairs of one of two types: short, capitate stalked glands, and subsessile peltate 'scales'. Inflorescences axillary or terminal, capitate to expanded, of simple or paniculate spikes or less often racemes; bracts simple, usually caducuous. Flowers bisexual or bisexual and male in same inflorescence or sometimes dioecious, 4- to 5-merous, actinomorphic or sometimes weakly zygomorphic, epigynous; hypanthium (receptacle) surrounding ovary (lower hypanthium) and extended beyond into saucer- to tube-shaped upper hypanthium bearing stamens and perianth, with 2 prophylls (bracteoles) fused to lower hypanthium in Laguncularieae; sepals 4-5, borne at tip of upper hypanthium, sometimes vestigial, rarely accrescent; petals 4-5, or often 0, free, alternating with sepals, usually borne at or near tip of upper hypanthium, often small, sometimes conspicuous; stamens usually twice as many as sepals, borne inside upper hypanthium usually at two levels, sometimes as many as sepals, antipetalous [or antisepalous] whorl missing, exserted or included, anthers 4-locular, dorsifixed, usually versatile, sometimes adnate; nectariferous disk, continuous or as separate lobes, often present at base of or at some distance up upper hypanthium; ovary 1-locular, ovules (1-)2-7, apical, pendulous, style 1, with usually punctiform stigma. Fruits indehiscent, with dry or spongy to succulent wall, often with 2-5papery to leathery wings; seed 1, endosperm absent, cotyledons usually 2, dorsiventral and variously folded or twisted (mostly spirally convolute or irregularly complicate), rarely conduplicate.

Distribution

Americas: present Guianas: present New World: present Southern America:, Venezuela (Venezuelapresent) throughout the tropics and subtropics of the whole world: present
About 500 species in 14 genera, distributed throughout the tropics and subtropics of the whole world; 5 genera occur in the New World and in the Guianas; of the 85 species in the Americas, 31 occur in the Guianas (plus 1 nearby in Venezuela).

Discussion

Unless otherwise stated, leaf length excludes the petiole, and flower length includes the ovary and calyx lobes but excludes the petals, stamens and style, and upper hypanthium length also includes the calyx lobes; upper hypanthium width is taken at junction of hypanthium and calyx lobes in Combretum, but includes the calyx lobes in Terminalia. The lower hypanthium is taken to include the ovary, any pedicel-like proximal region present, and the whole of any solid distal extension below the expanded upper hypanthium. All flower measurements are taken from boiled material; dried material is obviously smaller. Fruit length includes pseudostipe and beak where present, taken at midline; lateral extent of wing is described as wing-width. Leaf venation terminology follows Hickey (1973); descriptions refer to leaf lower surface unless indicated otherwise.

Taxonomy

Between 12 and 23 genera have been recognised in the past, the present author recognises 14 genera (Stace 2007a).
The genus Strephonema (West Africa) constitutes subfamily Strephonematoideae, the other 13 genera forming the Combretoideae. The latter is represented by 2 tribes, 1 of which has 2 subtribes; all 3 of these occur in the Guianas:
  • Laguncularieae: Laguncularia
  • Combreteae with 2 subtribes:
    • Combretinae: Combretum (including Thiloa)
    • Terminaliinae: Terminalia, Buchenavia and Conocarpus

Taxonomic changes

  • Combretum aubletii DC.

INTRODUCTION

The most recent global treatment of the wood anatomy of the COMBRETACEAE is by van Vliet (1979). Therefore, his descriptions were used as a basis for this chapter, supplemented by our own observations.
In van Vliet’s thorough study, each generic description was followed by an extensive discussion of the individual characters, their taxonomical value and their correlation with habit and habitat, and the classification of the family. Most of those data and conclusions go beyond the scope of this Flora. For example: when studying the bordered intervessel pits in COMBRETACEAE and allied families, van Vliet (1978, 1979) was able to distinguish between 2 main types, based on size of the vestures and their position in the pit chamber. One intervessel pit type (type A) was characteristic for the genus Strephonema Hook.f. (not studied here). The other type (type B), found in all other genera of COMBRETACEAE, was subdivided into 3 forms, but these subtypes were not correlated with other woodanatomical characters, nor did van Vliet find any correlation with the taxonomy of the family. Only in Terminalia the full variation of type B was found. As the use of a scanning electron microscope is essential to decide on the type of vesturing in a given sample, we refrained from describing the vesture types here. Moreover, a recapitulation here of van Vliet’s discussion of anatomical variation in relation to habit and habitat, but restricted to Guianan material only, would not contribute to, let alone improve, his conclusions and thus the reader is referred to the original work (van Vliet 1978).
Other quantitative characters that may be difficult to measure accurately from sections, such as vessel member length, ray height, are not given here, notwithstanding the fact they may have diagnostic value.
Van Vliet reports 2 distinct types of vessel elements for Combretum. Besides the elements typical for COMBRETACEAE, very narrow elements, often associated with vascular tracheids are present. In the Guianan species of Combretum, however, they are rarely found.
Descriptive terms and measurements are in accordance to the IAWA-list of microscopic features (1989).

FAMILY DESCRIPTION

Growth rings absent to distinct.
Vessels diffuse, round to oval, solitary and in short radial multiples of 2-3(-10); typical vessels in Combretum rarely intermingled with very narrow vessels and vascular tracheids in small clusters; mean tangential diameter 87-170 μm; 3-25 per mm². Perforations simple with horizontal to oblique end walls. Intervessel pits vestured, alternate, round to polygonal, (5-)6-9(-11) μm, rarely coalescent; vessel-ray pits similar to intervessel pits but half-bordered, sometimes in horizontal arrangement, elongate, rarely tending to scalariform or coalescent.
Rays exclusively uniseriate in Laguncularia, nearly so in Buchenavia, Combretum, Conocarpus and Terminalia. Rays composed of square and upright, and weakly procumbent cells in Buchenavia and Laguncularia.In Conocarpus upright to procumbent cells are intermingled. In Combretum and Terminalia, cells are procumbent (with infrequent square and upright cells and upright marginal cells); 7-11 per mm, but up to 20 in Combretum and Terminalia. Perforated ray cells present in Combretum.
Parenchyma apotracheal diffuse, sometimes in marginal bands or absent; paratracheal vasicentric to aliform-confluent, sometimes in bands of 2-5 cells wide; strands of (3-)4-7(-8) cells.
Ground tissue fibres thin-walled to very thick-walled; non-septate in Laguncularia, but septate in Buchenavia and Conocarpus. In Combretum and Terminalia, both septate and non-septate fibres can be found; pits simple to minutely bordered, mainly on radial cell walls.
Crystals present in rays and/or axial parenchyma, as small or large rhombic crystals, or as elongated rod- to styloid-like crystals, sometimes scanty (Table 1).
Table 1. Occurrence of crystals in Guianan COMBRETACEAE. Data between brackets: crystals are present in some species. ?: crystals have been reported by van Vliet (1979), but not confirmed in this study.raysaxial parenchyma
Buchenavia(rhombic, elongate)
Combretumsmall, rhombic in large ideoblastslarge, rhombic, in large ideoblasts
Conocarpuslarge, blunt prismatic, in radial rows
Laguncularialarge, prismatic to elongate
Terminalia(large, blunt prismatic)scanty rhombic; druses in T.catappa?

Wood

Five Guianan genera are represented, 2 of which by 1 species only.
Due to the variation within the large genera Combretum and Terminalia, it is impossible to separate these genera. However, some characters can be used for a preliminary identification purposes. Noteworthy here is that the radial vessels reported by van Vliet (1979) could not be found in our material.
The parenchyma pattern is variable, even within species. According to van Vliet, the diagnostic value is restricted to those species “where distinctly different types (e.g. aliform and banded) are compared”.
A. Détienne, P. & J. Jacquet. - in Atlas d’identification des bois de l’Amazonie et des régions voisines. 1983, B. Heimsch, C., Comparative anatomy of the secondary xylem in the Gruinales and Terebinthales of Wettstein with reference to taxonomic grouping in Lilloa 8. 1942, C. IAWA Committee., The IAWA list of microscopic features for hardwood identification in IAWA Bull. n.s. 10. 1989, D. Lens, F., S. Jansen, P. Caris, L. Serlet & E. Smets., Comparative wood anatomy of the primuloid clade (Ericales s.l.) in Syst. Bot. 30. 2005, E. Record, S.J. & R.W. Hess. - in Timbers of the New World. 1943, F. Record, S.J. & R.W. Hess., Identification of woods with conspicuous rays in Trop. Woods 48. 1936, G. Vliet, G.L.C.M. van, Radial vessels in rays in IAWA Bull. 3. 1976, H. Vliet, G.L.C.M. van, The vestured pits of Combretaceae and allied families in Acta Bot. Neerl. 27. 1978, I. Vliet, G.L.C.M. van, Wood anatomy of the Combretaceae in Blumea 25. 1979, J. in InsideWood. 2004-onwards

Notes

A full synonymy for all taxa is given in .