| Calliandra calothyrsus - Production and use: A Field Manual |
The genus Calliandra belongs to the family Leguminosae, subfamily Mimosoideae and tribe Ingae. Calliandra is a large genus with about 132 species from North and South America, 9 species from Madagascar, 2 species from Africa and 2 species from the Indian subcontinent. The center of diversity of the genus is in the state of Bahia, Brazil. There is a secondary center of diversity in southern Mexico and Guatemala. Many of these species are mostly shrubs or small trees, although occasionally they are herbs or larger trees (for example the species C. stipulaceae grows to 25 m). Most of the species do not have spines, although there are rare exceptions such as C. umbrosa from India.
Many species of Calliandra are found in humid lowland forest, often along river banks or in the forest understory. Some species, however, are found in montane vegetation (for example C. hirsuta), while others are found in arid scrub (for example C. californica).
Despite the broad range of localities and habitats in which Calliandra species occur, there are a number of features which make the genus easy to identify. The leaves of all species have a main axis from which secondary axes branch in pairs opposite one another. Pairs of leaflets are arranged along the secondary axes. On the leaves of some species there are only two secondary axes with a single pair of leaflets on each. On the leaves of other species there are numerous pairs of secondary axes and numerous pairs of leaflets. Uniquely, in a single Calliandra species, C. hymenaeodes leaflets branch off one central axis.
The flowers of all Calliandra species occur in clusters or semispherical heads. In some species these clusters are arranged in staggered groups towards the end of a flowering axis. The latter type of arrangement is called a raceme. The flowers themselves are almost always cup-shaped with five small petals arranged regularly. Many long white or red filaments extend beyond the floral cup. They are always joined into a tube at the base and are at least twice as long as the flower itself. Sometimes within the group of flowers in a head only the central few produce nectar and are functional. In these cases the outer flowers simple help to attract pollinators. In some species a small percentage of the flowers only have the male pollen producing parts, and these flowers are interspersed with bisexual flowers.
Calliandra flowers open at night and are usually pollinated by bats or moths which drink the nectar produced in the base of the floral cup. In the single species C. schultzei the flower petals are arranged irregularly and the principle pollinator is a species of hummingbird.
The fruit of all Calliandra species are straight (or slightly curved), flattened pods with raised margins. The pods split explosively from the tip to release seed. This particular mechanism of seed dispersal is found in only a few other genera, and in those genera it is always associated with very different floral structures. Appendix D gives morphological and seedling keys to the identification of some Calliandra species.
The species C. calothyrsus is unique within the genus in terms of its wide international use as an agroforestry multipurpose tree. It occurs naturally in Mexico and Central America from the state of Colima. Mexico. down to the north coast of central
Panama. In 1936 seed was sent from south Guatemala to Java in Indonesia. This seed was most probably collected from the Guatemalan provenance 'Santa Maria de Jesus'. By 1974, village based trials had been set up to assess the species suitability for the reforestation of eroded land around villages. C. calothyrsus proved well suited to a range of agroforestry systems and was promoted by the Indonesian state forestry sector for widespread planting. From Java it was introduced to many other Indonesian islands. Its popularity soon generated interest elsewhere and seed was sent to many countries in Africa, Asia and even back to Central America.
At the same time, in the early 1980s, the Costa Rican institute, CATIE, made a collection of seed from a limited number of provenances in Guatemala, Costa Rica and Honduras for trials in Central America.
In 1990 the Oxford Forestry Institute began a range wide collection of seed which was completed in 1993. The collection included 50 provenances from the eight countries within the species range. The seed was then sent out to 32 countries for the purpose of species and provenance evaluation. Consequently, populations of the species now exist in South America, Africa, Asia and Oceania and it can truly be said to have a pan-tropical distribution.
Calliandra calothyrsus is a small branching tree growing to a maximum height of 12 m and to a maximum basal stem diameter of 20 cm. The stems have red or pale gray bark covered in small, pale, oval lenticels. Towards the tip the stems tend to be ridged, and in trees with red-brown bark the final stem portion may be tinged with red coloring. Beneath the stem, the root system consists of several deep tap roots and a maze of finer roots which extend outwards just beneath the soil surface. In the presence of the correct rhizobia and mycorrhiza, nodules and fungal associations form. In some populations the species has been shown to develop from root suckers so that an apparent clump of bushes may in fact be one single individual.
The species has soft leaves divided into many straight leaflets. The leaves may reach 20 cm long and 15 cm wide and they fold against the stem at night. The leaf stalks are ridged with a groove on the upper surface, but they do not have glands between the pairs of secondary axes.
In the native range flowering occurs throughout the year, but it tends to peak between July and March. The inflorescence develops in a terminal position. Several clusters of flowers develop around nodes up the axis. The flowers mature from the base to the tip over a period of many months. The flowers open for a single night with showy filaments which are usually white at the very base and red at the tip (although they may exceptionally be pink). By the next day, the filaments have wilted and unfertilized flowers drop.
Pods take between two and four months to develop and when mature they may be 14 cm long and almost 2 cm wide. They are straight and mid-brown in color, and they contain 8-12 ovules which may develop into flattened oval seeds. The surface of mature seed is mottled brown and black, and it has a distinct marking in the shape of a horse shoe on both flattened surfaces. Mature seed reach 8 mm in length and are hard when pressed with a finger nail. In the native range, seed set peeks between the months of November and April. As the pods dry, tensions are created in the thickened pod margins which cause an explosive splitting from the tip. Seeds are ejected with a spinning motion and may fly up to 10 m.
The seedling develops with the two fleshy cotyledons above the ground. The first leaf has only a single axis from which leaflets develop, but subsequent leaves are divided into secondary axes.
The species has a number of common names in its local range, the most frequently used being 'cabello de angel' (meaning 'angel's hair') and 'barbe sol' (meaning 'the suns beard'). In Indonesia the species is referred to as 'Calliandra merah' (meaning 'red Calliandra').
In Mexico and Central America, C. calothyrsus is one of seven naturally occurring species within a section of the genus called 'series Racemosae'. The name Racemosae indicates that these species have an elongated flowering axis (up to 40 cm long). The leaves of these seven species are also distinctive since many pairs of secondary axes branch off the primary leaf axis, and each secondary axis has many pairs of small leaflets (less than 2 cm long and 0.5 cm wide). In South America there are many similar looking species, but they either do not have such long flowering axes, or they have fewer divisions of the leaves.
Calliandra calothyrsus can be distinguished from species of similar appearance by a unique combination of features. The species almost straight leaflets do not tend to overlap and they do not have a glossy upper surface. The leaves are soft and tend to fold when a leafy branch is cut. The small stipules (found in pairs at the base of the leaf stalk) are long and thin rather than oval, with a leafy texture when green. They almost always fall off on older stems. The stems, flowers and pods are almost always without hairs. The flower petals are delicate, smooth and green or pale yellow in color (rarely being tinged with red). The petals are never thick or woody and are never covered in hairs of any length or color.
Calliandra calothyrsus occurs naturally along river banks, but will rapidly colonize any area of disturbed vegetation (for example roadsides). It is not particularly tolerant of shade and may soon be out-competed in secondary vegetation. It inhabits a range of sites within Mexico and Central America from sea level to an altitude of 1860 m. It primarily occurs in areas with a mean annual rainfall of between 1000 and 4000 mm, although exceptional populations occur in areas with only 800 mm annual rainfall. It principally occurs in areas with 2-4 months dry season (with less than 50 mm rainfall per month). On occasions, however, specimens have been found in areas with a dry season as long as 6 months. It occupies areas with a mean annual minimum temperature of 18-22° C. It is not frost tolerant. Within its natural distribution it occurs on a variety of soils and appears to be tolerant of slightly acid soils with pH values around 4.5. It does not tolerate soils with poor drainage which are regularly inundated.
There is considerable morphological variation between different populations of C. calothyrsus. Certain geographical patterns present themselves, but the presence of numerous exceptions to these patterns has meant that no subspecies or varieties have yet been designated. Three particular trends of variation can be described.
Along the Pacific coast to the north of the isthmus of Tehuantepec in Mexico and in Central Honduras and Nicaragua there is a tendency for the species to have whiter bark, flowers with more white at the base of the filaments and sparse short hairs on slightly smaller pods. The areas in which this trend is found tend to be the drier portions of the species range.
In southern Mexico, Central Guatemala, Belize and northern Honduras there tend to be populations with red-brown bark, red flower filaments, and larger pods without any hairs. The trees in these populations tend to be taller in the native range, and occur in some of the wetter areas of the species natural distribution.
Finally, in similarly wet areas of Costa Rica and Panama populations tend to have leaves with more pairs of secondary axes.