Myristicaceae

Primary tabs

Myristicaceae

Description

Dioecious or monoecious (Endocomia) monopodial shrubs or trees with aromatic oil- cells, (2-)5-15(-40) m high (Virola sessilis, Brazil, 30 cm high); Hairs uniseriate, often with armed cells, appearing as stellate or dendroid. Leaves simple, entire, alternate, usually distichous in plagiotropic shoots, exstipulate, often with indumentum on both surfaces when young, glabrescent, or remaining on the lower surface; Inflorescences from foliar axils to ramiflorous (cauline), pedunculate, compound or not, with or without bracts at base, the flowers variably arranged at the ends of the branches, or a short, woody (sub)sessile simple or 2-4-fid scar-covered wart- or worm-like brachyblast with the flowers in (sub)umbels at the end; Flowers unisexual, mostly pedicellate; Ovary monocarpellate, sessile, superior, ovoid; Fruits (sub)globose to oblong, rarely transversely elongate, dehiscing by a longitudinal circumferential suture into 2 valves, rarely indehiscent; Seeds with testa of three layers;

Distribution

Africa: present America: present Asia-Tropical: Madagascar: present Papua New Guinea: present Southeast Asia: present from India to N Australia and far into the Pacific: present from India to W New Guinea: present from S China to New Guinea: present from S Peninsular Thailand to New Guinea: present from Sri Lanka and S China east to the Solomon Islands and N Australia: present
Pantropical with c. 500 species in 20 genera, more or less equally distributed over and restricted to the three main continental areas: 8 genera (with few species) in Africa, of which 5 in Africa proper and 3 in Madagascar, 6 genera in America, and 6 in Southeast Asia, mainly Malesia.

The largest genera are Virola (c. 50 species) in America, and Horsfieldia (c. 100 species), Knema (c. 90 species), and Myristica (c. 170 species) in Asia. The latter three, together with Endocomia and Gymnacranthera, have widespread distributions; Endocomia occurs from S China to New Guinea (), Gymnacranthera from S Peninsular Thailand to New Guinea (); Horsfieldia occurs from Sri Lanka and S China east to the Solomon Islands and N Australia, with centres of species richness in W Malesia, mainly Borneo and New Guinea (); Knema has a distribution from India to W New Guinea, with a centre of diversity in W Malesia, mainly Borneo (); the genus Myristica has the largest distribution, from India to N Australia and far into the Pacific, with centres of speciation in W Malesia and, particularly, New Guinea (100 species) (). Paramyristica (1 species) is endemic to Papua New Guinea ().

In the present treatment the now official name Papua Barat has been used instead of Irian Jaya.

Anatomy

A detailed description of the leaf anatomy of the Asian Myristicaceae was given by Koster & Baas (1981). For short leaf anatomical accounts see also Schouten (1986) and De Wilde (1994). Metcalfe (1987) summarized the vegetative anatomy of the whole family. For the present survey more specimens were examined, including the two new genera Endocomia and Paramyristica.

About 65 of the species belonging to the six Asian genera have been examined leaf anatomically. Individual species will not be mentioned in this synopsis, although many of the species examined can be distinguished by their leaf anatomical characters. Genera will be mentioned when a character has diagnostic value on the genus level.

Hairs are present, at least in young leaves, on both surfaces or only on the abaxial surface (in Gymnacranthera and some Myristica species). A hair is composed of one row of short to tall cells, having one or two arms each, one or two (rarely more) cells nearest the epidermis (the so-called stalk cells) excepted. In Gymnacranthera, Myristica, and Paramyristica the cells have two arms, of unequal length in Gymnacranthera; the cells in Endocomia, Horsfieldia, and Knema have one arm. In older leaves the hairs have often been shed, but the upright walls of the most proximal parts remain as cutinized rings on the epidermis. These rings are subtended by one to numerous small cells, arranged in a circle or oval.

Alveolar material, as an irregularly structured cutinaceous layer overlying the cuticle proper, is present on the abaxial side in many species. The thickness of the cuticle proper measures up to 18 µm adaxially and to 11 µm abaxially. The cuticular flanges on the ad- axial surface are usually more or less sinuous at high focus and more or less straight at lower focus; thin areas of cuticle are present in the loops of the undulations. The cuticular flanges usually show inconspicuous pitting.

Abaxial papillae sometimes occur. Large empty idioblasts (partially) with a thin cuticle or without a cuticle, probably secretory cells, are often present. Some species abound in regular cork warts; groups of basal cells of hairs are probably the origin of some of these structures.

Stomata are usually confined to the abaxial epidermis; the stomatal type is paracytic. The dimensions of the guard cell pairs range from 8 to 21 µm for the width and from 15 to 39 µm for the length. The guard cells are often embedded in the subsidiary cells, which are dome-shaped in Gymnacranthera. In Knema, Myristica, and Paramyristica the stomatal complex is (strongly) sunken; the bordering epidermal cells show papillae. In Knema and some species of Myristica these papillae are more or less horizontally directed, leaving a star-shaped opening above the stomatal complex. In most species of Myristica and in Paramyristica the more or less upright papillae form a ring above the stomatal complex.

An adaxial hypodermis is sometimes present, either as a continuous layer or only locally. An inconspicuous abaxial hypodermis has been recorded for a few species.

The mesophyll is dorsiventral (rarely isobilateral), with mostly two or three, sometimes up to four adaxial layers of palisade parenchyma. In the leaf margin the cells adjacent to the epidermis often have sclerified walls.

The midrib is abaxially prominently raised, and adaxially raised in most Horsfieldia species, in Endocomia, Knema, Myristica, and Paramyristica. There is a more or less straight adaxial vascular bundle (sometimes strongly interrupted) and an arc-shaped abaxial bundle, sometimes joined together. The phloem is arranged in separate strands, often in two layers. One to numerous phloem bundles are interspersed in the ground tissue between the main bundles, often accompanied by xylem elements; in some Knema species there is a complete collateral bundle in the pith. In Gymnacranthera the adaxial bundle is absent. The whole system is surrounded by groups of sclerenchyma fibres, which also occur in the pith, often even in the centre of the phloem bundles. The ground tissue is from centre to periphery parenchymatous to collenchymatous, often interspersed with cells with sclerified walls; in Gymnacranthera and Knema there are often several layers of these cells at the periphery of the midrib. Sometimes adaxial chlorenchyma is continuous in the midrib.

The veins are supplied with collateral bundles; the major veins may have a more complex vascular system, not unlike that of the midrib. Sclerenchyma caps are present at the abaxial and adaxial sides; in Knema a sclerenchymatous bundle sheath is found. A usually poorly differentiated parenchymatous bundle sheath, in Knema sometimes continuous to the epidermides, surrounds the bundle and the sclerenchyma. In Knema strands are present, consisting of sclerenchyma fibres only, in position and distribution not unlike the vein bundles.

The petiole at its basal end has a vascular system consisting of three more or less arc- shaped collateral bundles with free phloem bundles adaxially. The sclerenchyma is usually confined for the greater part to the abaxial sides. The vascular system of the distal end is intermediate between that of the basal end and the midrib.

Crystals may be present in various types. Large druses in enlarged mesophyll idioblasts frequently occur, often adjacent to epidermal cells, which may be extremely flattened and have a thin cuticle and thin and short cuticular flanges (in Myristica adaxially and in Endocomia, Gymnacranthera, and Horsfieldia adaxially and abaxially). Small druses have also been found, but not in Gymnacranthera. Small spindle-shaped particles often occur, usually grouped in cells of the mesophyll and the ground tissue of the midrib. Other crystal types have been found in one or a few species only.

Large, more or less spherical cells frequently occur in the mesophyll and the ground tissue of the midrib. Usually they contain oil, in some species probably tannin- or muci- lage-like substances. The large empty idioblasts in the epidermis have been mentioned above. Fairly thick-walled tubule-shaped cells have sometimes been found, adaxially and abaxially of the sclerenchyma caps of the vein bundles. The content of these cells is probably tannin.

Sclereids are often present as brachy- to astrosclereids in the ground tissue of the midrib. Filiform, rarely branched sclereids have been recorded for Gymnacranthera. Astrosclereids and thick filiform, branched sclereids are present in a few species only. The genera Gymnacranthera and Knema can be distinguished by a combination of leaf anatomical characters. Leaf anatomy provides no means to discriminate between Endocomia and Horsfieldia and between Myristica and Paramyristica.

Wood anatomy — The wood anatomy of the Myristicaceae is fairly uniform. For a detailed family description and literature survey see Metcalfe (1987). Wood anatomy of the main Malesian genera is summarized in the Prosea Handbooks 5: 2 & 3 (Lemmens et al. 1995; Sosef et al. 1998) and pictured by Ilic (1991). The wood is diffuse-porous with vessels medium-sized and in low density (usually 3-12/sq.mm), solitary and in radial multiples. Perforations mixed simple and scalariform, but one of the types dominant or (virtually) exclusive in some species. Intervessel pits ranging from scalariform to opposite and alternate. Vessel-ray pits often coarse and with reduced borders to simple. Fibres thin- to medium thick-walled, with minutely bordered to simple pits, often septate around the vessels. Parenchyma scanty paratracheal to narrowly vasicentric and often also in zonate bands. Rays typically l-2(-3)-seriate, heterocellular and composed of fairly large cells. Crystals present in ray cells or absent. Tanniniferous tubes, usually in very low frequency, present in all species studied, and virtually unique to the family Myristicaceae (except sporadic occurrence in some members of the Ulmaceae). Oil and/ or mucilage cells present among the axial and ray parenchyma in some species.
1. J. Koster, leaf anatomy & P. Baas, wood anatomy

Taxonomy

The family Myristicaceae is homogeneous and clearly belongs (also phytochemically) within the Magnoliales. Phylogenetic analysis of the genera revealed that the family is monophyletic, of African origin (Sauquet 1998), and seemingly most related to the Annonaceae, mainly through the ruminate endosperm. Canellaceae have been suggested to be allied through the monadelphous androecium (Wilson & Maculans 1967), but according to a recent cladistic analysis of all families (APG 1998) this family is as yet not properly placed as it falls beyond the recognized basal orders. The foliage is generally strongly reminiscent of Annonaceae. The 3-lobed perianth reminds of Lauraceae and Annonaceae. Myristicaceae are distinguished, however, by their unisexual flowers with uniseriate perianth, and monocarpellate 1-ovuled female flowers.

Within the family the relationship of the genera is unclear, and initially one single genus, Myristica (divided into sections), was recognized until Warburg (1897) divided it into several genera. The genera of Madagascar possibly retain the most primitive characters, viz. pollen morphological, not or less consolidated stamens, and a little developed aril.

Within the larger Malesian genera, Horsfieldia, Knema, and Myristica, subgenera or series have been recognized (Warburg 1897; Uphof 1959; Sinclair 1968; De Wilde 1979), but as explained under these genera, the distinctions are not sharp and only allow for informal grouping of species, largely reflected in the keys to the species.

Cytology

According to the summary presented by Kühn & Kubitzki (1993), based on Marawetz (1986), and Plant Resources of South-East Asia 5 (2, 1995 & 3, 1998), chromosome numbers are high and interpreted as (paleo)polyploid. Known are for Knema: 2n = 42 (K. intermedia: n = 21), Gymnacranthera: 2n = 44 (G. farquhariana var. zippeliana: n = 21), Horsfieldia: 2n = 50 (H. iryaghedhi: n = 25), Myristica: 2n = 42 or 44 (M. elliptica: n = 21, M. fragrans 2n = 42). In the New World much higher numbers have been found (Osteophloeum: 2n = c. 280).

Uses

In most myristicaceous species the heartwood is poorly differentiated from the sapwood, and the wood is of minor commercial importance. The timber is suitable for temporary light constructions. The wood, mainly from the blackish-stemmed group (including Myristica lowiana), is mostly soft or moderately hard or heavy; perishable, but easily treated with preservatives; it is easy to work, but sometimes splits soon. The sapwood is pale, sometimes not well defined, but often the heartwood is dark reddish brown.

The seeds of some species may be used for their fat content or their fragrance, also as medicine. Myristica fragrans is most important, yielding nutmeg (seeds), mace (aril), and the spicy pericarp can be candied. The seeds of M. argentea (W New Guinea) is of minor importance.

Myristicaceae are rarely used in silviculture. Some data are given in PROSEA 5 (2, 1995 & 3, 1998). Propagation is by seed, and shade should be provided for germination and growth. A few species are ornamental (e.g., Horsfieldia iryaghedhi), or may be introduced as such (e.g., H. sylvestris)

Citation

W. J. de Wilde - in Blumea. 1994
R.Br. - in Soepadmo & Saw (eds.), Tree Fl. Sabah & Sarawak 3. 2000
Kühn & Kubitzki - in Kubitzki et al., Fam. & Genera Vascular Plants 2. 1993
Warb. - Monographie der Myristicaceae in Nova Acta Acad. Caes. Leop.-Carol. 1897
J. Sinclair - in Gard. Bull. Sing. 1958: pl. I-XIV
R.Br. - in Beitr. Biol. Pflanzen. '1991', 1992
W. J. de Wilde - in Blumea. 1984
Whitmore - in Tree Fl. Malaya. 1972