Mimosaceae

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Mimosaceae

Description

The majority of the Malesian genera are shrubs or small to large trees. Herbs are represented by the genera Neptunia and Mimosa p.p. Climbers are found in Acacia subg. Aculeiferum, in 3 species of the genus Albizia, A. corniculata, A. myriophylla, and A. rufa, and in Entada. Oldeman (1989) gave an account on the biological implications of leguminous tree architecture. Acacia auriculiformis as studied in Indonesia by Edelin (1984) has as a young tree a monopodial, orthotropic trunk. When having reached a certain developmental stage (which may vary considerably according to age and size of the trees), the original model is reiterated at the place of certain branches, the apical meristems of which begin to function accordingly. When the tree grows still higher, the extremity of the original trunk bends over, height growth is taken over by one of the branched models somewhere on the curved trunk, and this process continues (Oldeman I.e.). It is concluded that the complex and flexible architecture of leguminous trees allows them to survive in complex and unstable environments. An example of a species that remains unbranched throughout its lifetime is Archidendron glabrum (Hallé et al. 1978, sub Pithecellobium hansemannii).
Trees, shrubs or lianas, very rarely herbs (Neptunia and Mimosa p.p.); Leaves alternate, usually bipinnate (unipinnate in Inga, transformed into phyllodes in Acacia subg. Phyllodineae), usually provided with extrafloral nectaries on rachis and pinnae. Stipules rarely absent, usually caducous. Inflorescences bracteate, simple or compound, racemose; Flowers actinomorphic, bisexual, unisexual, or rarely neuter, usually small and white, greenish or yellow. Stamens few to numerous, free or united into a tube, the latter sometimes united with the corolla-tube at the base. Ovary(-ies) solitary (to several and free), superior, 1-celled; Ovules anatropous, parietal. Fruit a pod, dehiscent or indehiscent, sometimes breaking into 1-seeded segments. Seeds usually in two rows from the single placenta, inserted transversely, obliquely or longitudinally, mostly ovate-orbicular in outline, often compressed;

Distribution

Africa: present America: present Asia: present Asia-Tropical:, Indiapresent; Philippines (Philippinespresent); Thailand (Thailandpresent) Australasia: Burma: present Central and N tropical South America: present E Malesia: present Madagascar: present Melanesia: present N Celebes: present New Caledonia: present Pantropical: present Solomon Islands: present South America: present Tropical Africa: present W Pacific: present continental S Asia: present mainland Asia: present tropical (to subtropical) Australia: present tropical America: present tropical Asia: present tropical Central/South America: present tropical N Australia: present west Pacific: present
About 60 genera and some 3000 species, mainly in the tropics and the subtropics, but some genera (e. g. Acacia and Albizia) extending into the warm-temperate zone; in Malesia: 19 genera, of which 15 native, with 1 endemic, viz. Wallaceodendron in N Celebes and the Philippines. Among the remaining 14 native genera, 5 are pantropical (Acacia, Albizia, Entada, Neptunia, Parkia), 3 are shared with continental S Asia and tropical N Australia (Adenanthera, Archidendron, Cathormion), 2 with Melanesia and the west Pacific (Schleinitzia, Serianthes), 2 with Australia (Pararchidendron, Paraserian- thes), 1 with New Caledonia, the Solomon Islands and Australia (Archidendropsis), and 1 with India and tropical Africa/Madagascar (Dichrostachys). The total number of native and naturalized species is c. 150. Furthermore, an enumeration of c. 45 cultivated species is given at the end of this revision (p. 205). In both Keys to the genera 7 commonly cultivated genera are included.
In the family Mimosaceae tropical Asia and Australia have close affinities, a number of species being common to E Malesia and tropical (to subtropical) Australia. The links between Asia and Africa are weak, although a few species (Acacia nilotica, Dichrostachys cinerea, Entada rheedii) and a part of the very diversified genus Calliandra are common to both continents. Other links between Asia and Africa are Xylia from India / Burma to Thailand/Indochina and the rest of the species in Africa / Madagascar and the genera of the Adenanthera group, Adenanthera being endemic to Asia — Australia and Tetrapleura and Amblygonocarpus to tropical Africa. The only generic tie between Asia and tropical America is the not yet fully understood Havardia: 3 species in mainland Asia, the remaining c. 20 in Central and N tropical South America (Nielsen 1981). More distantly related 'sister groups' are Arc hide ndron, which is related to the tropical American genus Cojoba (Nielsen et al. 1984), and Schleinitzia with the American genus Leucaena (Lewis & Elias 1982). Africa and America share only 2 non-pantropical genera, 12 genera being endemic to Africa/Madagascar and 27 to America. Indopiptadenia is the only genus endemic to mainland Asia.
A few species-rich genera as Acacia (more than 1300 species), Calliandra (c. 200), Inga (c. 350), and Mimosa (c. 400) account for the major part of the diversity, a fact that cannot be explained by differences in generic concepts alone; it is a testimony that adaptive radiations have taken place in Australia (Acacia) and in South America (Calliandra, Inga, Mimosa). The number of monotypic genera is low; in Malesia: Wallaceodendron; in Malesia/Australia: Pararchidendron; in India: Indopiptadenia\ in Africa/Madagascar 5, and in America 6 genera.
The family, with five pantropical genera, thus displays a complicated distribution pattern of widely distributed genera and narrowly distributed relictual ones. The first genera evolved are probably those of the tribe Mimoseae, the centre of origin being Africa/ America, and the tribe Parkieae. Then Acacia developed in the everwet tropics from ancestors like subg. Aculeiferum, being followed by the evolution of Acacia subg. Acacia and subg. Phyllodineae in the arid areas of the tropics and subtropics. Tribe Ingeae has two centres of evolution, both in the everwet tropics, one in tropical Central/South America and one in tropical Asia/W Pacific.
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Pollination

Probably most species are bee- and/or butterfly-pollinated, e.g. almost all species of Acacia, Albizia, Calliandra, and Mimosa. The genus Parkia is bat-pollinated (p. 195). Ornithophily has been recorded from some New World Mimosaceae (Abarema, Albizia, Calliandra, Inga, Samanea) and from Acacia nilotica in India (Arroyo 1981) and Africa.

Dispersal

The dispersal unit of the Mimosaceae is either the whole pod, as in species with indehiscent pods of Acacia, Albizia, Enterolobium, Samanea, Serianthes and Schlei- nitzia, or 1-seeded segments of the pod as in Cathormion, Entada, Mimosa, Wallaceoden- dron, or the seed in the genera Adenanthera, Dichrostachys, Leucaena, Neptunia, Parkia, dehiscent species of Acacia, Albizia, Archidendron, Archidendropsis, Par archidendron, and Paraserianthes. The dispersal agents are water and wind. The 1-seeded segments of Entada phaseoloides and E. rheedii can be widely dispersed by rivers and sea-currents as are the indehiscent pods of Serianthes grandiflora, a species mainly found on off-shore islands and occurring throughout Malesia but not yet known from tropical Australia, unlike Cathormion umbellatum, which is found in moist habitats and in associations behind the mangrove from mainland Asia through Malesia to N Australia. The Pacific genus Schleinitzia p.p. and Albizia retusa have thinner pods and are also sea-dispersed. Wind- dispersal has been recorded for some species of Acacia that have samaras. Albizia pedicellata also has samaras, and is probably wind-dispersed. Most species of Archidendropsis have flattened seeds with a narrow wing. They have not yet been observed as wind- dispersed, but probably are (Nielsen et al. 1983; Gunn 1984). In Wallaceodendron the one-seeded endocarp segments are adapted to wind-dispersal (Augspurger 1989). The species of Archidendropsis and Wallaceodendron do not have very wide distributions, whereas Albizia pedicellata has a wider area of distribution (Malaya, Sumatra, Borneo, Philippines). The size of landmasses and the distances to be bridged over open sea explain these differences in distribution patterns and wind-dispersal does not seem to be longdistance dispersal in Malesian Mimosaceae. Endozoochorous dispersal is frequent in species with indehiscent pods as e.g. Acacia nilotica, where one tree can produce more than 30,000 seeds in one fruiting season (Tybirk 1989) and the pods are eaten by cattle and other ruminates, the germination being promoted by the passage through the digestive system. Many seeds in this and other hard-seeded species are destructed by Bruchid weevils, highly host-specific seed predators. Endozoochoric dispersal has also been observed in Adenanthera pavonina, where fruit-eating birds feed on the red, hard, mimetic seeds but are unable to break the seed coat and defecate them intact, while granivorous birds refuse them (Van der Pijl 1982). Ornithochory probably also plays an important role in the dispersal of Archidendron and Par archidendron, with the bluish-black seeds contrasting with the orange-red endocarp in most species (Nielsen et al. 1984). Ornithochory also is important in species with arillate seeds such as in Acacia subg. Phyllodineae p.p. and American Pithecellobium. Ant dispersal plays a role in Australian and probably also in New Guinea species of Acacia with arillate seeds (Van Staden et al. 1989). Small mammals probably disperse large-seeded species such as Archidendron jiringa and Entada spiralis.

Biologically the genera of Mimosaceae can be divided into two groups: those with seeds with a hard seed coat and those with short-lived, 'recalcitrant' seeds. The genera with seeds with a hard seed coat have an outer layer which consists of a palissade layer of Malpighian cells with a 'light line', but often also of one or two layers of 'hour-glass' cells (Corner 1951, 1976; Nielsen et al. 1983; Gunn 1984; Maumont 1990). These seeds also have a pleurogram on the outer surface. The seeds of this group have a very long dormancy, the hard seed coat protecting the embryo against desiccation, physical damage and damage by predators. In at least some cases it acts as a regulator of the size of the seedling populations as the seeds only germinate in case of scarification of the seed coat after, for instance, the passage through the guts of cattle or the extreme heat caused by forest fires (e. g. Acacia p.p. and Paraserianthes lophantha in Australia and Java; Cavanagh 1980; Van Steenis 1972). Seeds with hard seed coats are found in the tribes Acacieae, Ingeae p.p., Mimoseae, Mimozygantheae, and Parkieae. In Malesia the following genera of tribe Ingeae have a hard seed coat with pleurogram: Albizia, Cathormion, Pararchiden- dron, Paraserianthes, Samanea, Serianthes, and Wallaceodendron.

In the Malesian genera Archidendron and Archidendropsis very short-lived, so-called recalcitrant seeds are found. These seeds are so short-lived that they sometimes germinate in the pod (some species of Malesian Archidendron and New Caledonian Archidendropsis). The seeds of these two genera and also of the American genera Cojoba and Zygia are often 'overgrown', as termed by Corner, and have large amounts of nutrition securing the developing seedling in everwet habitats for a long period.
A. Alexander, I.J. - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, B. Arroyo, M.T.K. - in Advances in Legume Systematics. 1981, C. Augspurger, C.K. - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, D. Bawa, K.S. & D.P. Buckly - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, E. Bernhardt, P. - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, F. Cavanagh, A.K. in Proc. Roy. Soc. Victoria 91. 1980, G. Corby, H.D.L. - in Advances in Legume Systematics. 1981, H. Corner, E.J.H. in Phytomorphology 1. 1951, I. Edelin, C. - in L'Architecture monopodiale, l'example de quelques arbres d'Asie tropicale. 1984, J. Gunn, C.R. in U.S. Dept. Agric. Techn. Bull. 1681. 1984, K. Hallé, F., R.A.A. Oldeman & P.B. Tomlinson - in Tropical Trees and Forests, an architectural analysis. 1978, L. Kenrick, J. & R.B. Knox - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, M. Maumont, S. - in Interet taxonomique de l'histologie des teguments seminaux chez les Acacieae et les Ingeae (Leguminosae-Mimosoideae). 1990, N. McKey, D. - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, O. Nielsen, I., Ph. Guinet & T. Baretta-Kuipers, Bull. Mus. Nam. Hist. Nat. Paris in Adansonia no. 3. 1983, P. Nielsen, I., T. Baretta-Kuipers & Ph. Guinet in Opera Bot. 76. 1984, Q. Oldeman, R. A. A. - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, R. Pijl, L. van der - in Principles of dispersal in higher plants. 1982, S. Schrire, B.D. - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, T. Sprent, J.I., J.M. Sutherland & S.M. de Faria - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, U. Staden, J. van, J.C. Manning & K.M. Kelly - in Monogr. Syst. Bot. Missouri Bot. Gard. 1989, V. Steenis, C.G.G.J. van - in Mountain Fl. Java. 1972, W. The seeds of the dicotyledons in - undefined journal - 2 vols. 1976, X. Tybirk, K. in Nordic J. Bot. 9. 1989, Y. Vogel, E.F. de - in Seedlings of dicotyledons. 1980

Anatomy

The following is summarized from Metcalfe & Chalk's (1950) general survey of the anatomy of the Mimosaceae, extended by data from more recent publications cited below. The anatomical diversity of the Malesian representatives is only incompletely known and further study will certainly provide markers of taxonomic interest.

Taxonomy

Most of the fundamental work by G. Bentham (1875) is still valid, at tribal as well as at generic and specific level. He recognized ". 7 tribes or collective genera, and 46 genera or subgenera" (I.c.: 343). Tribes 1. Pentaclethra and 2. Parkia were defined by the imbricate sepals, a character pointing towards a relationship with the caesal- pinioid genus Dimorphandra and its allies (e. g. the Malesian genus Sympetalandra). Hutchinson (1964) and Elias (1981) considered them as belonging to one tribe named Parkieae and also accepted the tribe Mimozygantheae, based on the Argentinian monotypic genus Mimozyganthus, which has imbricate and free sepals. In Bentham (I.c.) the three following tribes, 3. Piptadenieae, 4. Adenanthereae and 5. Mimoseae, have valvate sepals and a definite number of stamens. In the Piptadenieae the seeds have no albumen, but the anthers have a stipitate gland at the apex of the connective as in most of the Adenanthereae, which have albuminous seeds. Tribe 5. Mimoseae has anthers usually without glands and albuminous seeds. Hutchinson (1964) united the Piptadenieae and Adenanthereae as the distinction between them broke down after the study of new material. Finally Lewis & Elias (1981) united all the species with valvate sepals and a definite (< 10) number of free stamens into one tribe: the Mimoseae. The fruit and seed characters play an important role in tribe Mimoseae where 38 genera with more than 720 species are now recognized and in which the American/African/Indian genus Mimosa accounts for some 350-400 species.

In tribe Acacieae, which has been kept since Bentham (I.c.), the stamens are free, only exceptionally connate at the base (the African Faidherbia albida) (see also Vassal 1981). Two of the subgenera, Acacia and Aculeiferum, have many species with anther glands similar to the ones found in many Mimoseae. The glands are lacking in the third subgenus, Phyllodineae, and in the American section Filicinae of subgenus Aculeiferum. The species of section Filicinae, moreover, lack extrafloral nectaries on the leaves, they are unarmed, and the floral pedicel is jointed (as in Adenanthera) and will probably prove to belong to a distinct subgenus of Acacia. Recently Pedley (1986) proposed to divide the classical genus Acacia into three genera: Acacia (= Acacia series Gummiferae Benth.), Racosperma Mart. (Acacia series Phyllodineae Benth.) and Senegalia Raf. (Acacia series Vulgares Benth.). However, the characters presented by Pedley give evidence for a division into two genera, Acacia and another combining Racosperma and Senegalia, and until the American species have been compared with the Australian species, it seems better to keep the large genus Acacia with more than 1300 species intact. Moreover, the three genera proposed seem to be closer related to each other than to the rest of the Mimosoideae, and the discussion is then a question of rank. Species as Acacia harmandiana of Indochina and Thailand with 15-22 stamens and A. leucophloea with 20-25 stamens and glandular anthers could belong to the oldest part of subgenus Acacia, showing convergence in characters to those of the Mimoseae. The number of Acacia species is low in Malesia as compared to Australia, and the disjunct distributional areas of some members of subg. Aculeiferum (Nielsen 1985) and Acacia (A. tomentosa and A. leucophloea) of mainland Asia and those of species of subgenus Phyllodineae common to New Guinea and Australia clearly show that the Malesian Acacia flora is of dual origin: W Malesia/mainland Asia and New Guinea/Australia, the two elements meeting in the Lesser Sunda Islands.

In tribe Ingeae, defined by the indefinite number of stamens which are fused to a tube at the base, Bentham recognized "15 genera or subgenera" (I.e.: 343) with 408 species. At present some 20 genera and c. 1000 mostly tropical species are recognized (Nielsen 1981). Unlike Acacia, which has spread into the semiarid regions of the tropics and which there plays an important phytosociological role, the major part of the Ingeae is found in the humid part of the tropics, although a few genera (e.g. Albizia) extend into semiarid and warm temperate regions as well and have developed deciduous species.

Cytology

Goldblatt (1981) reviewed the basic chromosome numbers of the Mimosaceae; x = 14 and x = 13 are the widespread numbers. Tetraploids and/or octaploids have been recorded in the genera Schleinitzia, x = 27, 26; Dichrostachys and Acacia subg. Acacia. (A. farnesiana, 2n = 52, 104; A. leucophloea, 2n = 52), Adenanthera pavonina (26, 64?), Mimosa pudica (32, 48,52), Neptunia oleracea (52, 54) (see also Nielsen 1981). Several counts need confirmation. During my recent study for Archidendron grandiflorum 2n = 26 was counted (no 89 BI00472, ex Australia, AAU).

Uses

Several exotic species of the Mimosaceae have been introduced as ornamentals and/or shade-trees, cover-crops, sources of firewood etc. The introduced species are of either Australian (Acacia) or American (Acacia, Albizia, Calliandra, Inga, Leucaena, Mimosa, Pithecellobium, Prosopis) origin. The well-established naturalized species have been included in this treatment, the most common, non-naturalized ones have been included in the keys only with a note on the geographical origin (see also Backer & Bakhuizen f. 1963, for keys and short descriptions of the introduced species). Seeds and pods of Archidendron bubalinum, A.jiringa and Parkia speciosa are very often seen in town markets of W Malesia, as are the floating stems of Neptunia oleracea that are used as a vegetable. The fast-growing Leucaena leucocephala (National Academy of Sciences 1979), a native of tropical America, is used in reafforestation projects. One of the fastest growing trees of the tropics, Paraserianthes falcataria, originates from E Malesia and is an important source for paper pulp. It is very often planted as a shade-tree as well, although the roots grow superficially and spread widely, and the tree starts to decay at a rather young age (c. 10 years) dropping the branches on the crop it covers, causing considerable damage. The species of Mimosa, originally imported as cover-crops to prevent erosion, have now become serious weeds and thus of adverse economic importance.

Important timber trees are Albizia acle of the Philippines and Acacia mangium of East Malesia/Australia. The latter species is now widely used in reafforestation projects. Some of the Albizia species of the everwet areas of W Malesia (e.g. A. pedicellata, A. rosulata, A. splendens) deserve wider recognition. The saponin contents of the wood and bark of Albizia acle and A. saponaria is high. The latter has been used as soap and as fish poison (Burkill 1966).

Amongst the ornamentals the South American Samanea saman, the 'Rain Tree', is the most widespread and, together with the Madagascan Delonix regia, the 'Flame of the Forest" (Caesalpiniaceae), the most common street tree in Malesia. Acacia auriculiformis of New Guinea/ Australia is also widespread, especially in regions with a seasonal climate.

For further information about uses, consult Heyne (1927), Corner (1940), and Burkill (1966), and the notes under genera and species.