Canthium (PROSEA Timbers)

Plant Resources of South-East Asia
Introduction

Protologue: Encycl. Meth., Bot. 1: 602 (1785).

Family: Rubiaceae

Chromosome number: x= unknown; 2n= 44 for several African and Indian species

Origin and geographic distribution

Canthium in the broad sense is a large genus of over 200 species which occurs in the African and Asian tropics. In Asia Canthium sensu stricto is restricted to India, Sri Lanka, Burma (Myanmar), Indo-China, southern China, Thailand and western Malesia (east to the Philippines, Borneo and Java). Several dozen species are found in Malesia, but most of these are shrubs, small trees or climbers and only a few reach timber size.

Uses

The wood of Canthium is used locally in house and boat building, and for flooring and implements.

Production and international trade

Utilization of the wood is only local and very limited because the trees are usually small and scattered.

Properties

Most of the following information refers to species identified as belonging to Psydrax from Malaysia and the Philippines, but which most probably applies to species of Canthium . Usually they yield a medium-weight hardwood. Indonesian samples of Canthium species are medium-weight to heavy hardwoods with a density of 560-1060 kg/m³at 15% moisture content. Heartwood pink when fresh, turning pale brown or orange-brown with age, not distinct from the paler sapwood; grain straight; texture very fine and even. Growth rings indistinct or sometimes visible to the naked eye, marked by vessel-free zones; vessels very small to medium-sized, almost exclusively solitary but with occasional radial pairs, open; parenchyma moderately abundant, indistinct with a hand lens, apotracheal diffuse or diffuse-in-aggregates, or scanty paratracheal; rays extremely fine and moderately fine; ripple marks absent.

The wood is very hard and that of the Indonesian Canthium species is strong and moderately durable.

See also the table on microscopic wood anatomy.

Botany

Spiny or unarmed climbers or shrubs to small or medium-sized trees up to 25 m tall; bole usually straight; bark surface smooth to irregularly fissured or cracking, sometimes lenticellate, greyish-brown, inner bark brown. Leaves opposite, simple, entire, short-stalked; stipules triangular. Flowers axillary, solitary or in a stalked cyme-like or umbel-like inflorescence, 4-5(-6)-merous; calyx with triangular lobes; corolla with a short tube and valvate lobes; stamens inserted in the throat of the corolla tube; ovary inferior; style with globose to cylindrical stigma. Fruit berry-like, ovoid, obovoid to globose, often strongly bilobed and slightly laterally compressed. Seed plano-convex. Seedling with epigeal germination; cotyledons leafy, green.

In Java C. glabrum flowers almost throughout the year. The trees usually have a straight trunk with evenly spaced pairs of horizontal main branches.

Canthium belongs to the tribe Vanguerieae which is renowned for its very closely related genera with poorly defined limits. Many genera have been split off from Canthium in the broad sense, such as the South-East Asian genera Meyna , Perakanthus and Psydrax (the latter is also present in Africa, the Pacific and Australia). Psydrax has several species which grow to timber size. Many Psydrax specimens belonging to species collected in Malesia have been named Canthium didymum Gaertn. or Canthium diococcum (Gaertn.) Merr. However, the true Psydrax diococca Gaertn. (synonym: Canthium didymum ) occurs only in Sri Lanka and southern India. Research is needed to decide whether some of the species treated here under Canthium , i.e. C. lucidulum and C. sumatranum , belong to Canthium sensu stricto or to one of the related genera.

Ecology

Canthium trees occur scattered, mainly in lowland or sometimes in lower montane forest up to 1000 m altitude.

Silviculture Canthium may be raised from seed. For C. glabrum there are 4950-5600 dry seeds/kg. Only about 25% of the fruits of C. glabrum sown germinate in 43-123 days.

Prospects

Knowledge of Canthium and related genera is scarce. A taxonomic revision of the genera and species for South-East Asia, therefore, is required to interpret the literature and to serve as a basis for further research. On the other hand, most species are economically of no interest since they seldom reach merchantable size.

Literature

70, 144, 145, 163, 209, 267, 405, 436, 543, 716, 829, 831, 861, 934, 1221.