Olacaceae

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Olacaceae

Description

Trees or erect, rarely scandent shrubs, sometimes hemi-, rarely autoparasitic. Leaves spirally arranged, rarely distichous, simple, entire, often with parchment-like and/or finely tuberculate surfaces, mostly penni-, rarely pli-nerved, petioled, exstipulate, not rarely of a greyish-yellowish-olivaceous colour and dull, especially in the dry state. Inflorescences axillary, rarely on old wood, short racemes and panicles, or elongate spikes, often fascicles or glomerules, these rarely reduced to a solitary flower. Flowers generally bisexual, rarely unisexual (monoecious or andro-dioecious), generally actinomorphic, cyclic, 3-7-merous, rarely heterostylous. Petals 3-7, free or connate below, valvate, caducous. Stamens 1 — 3-seriate, hypogynous, 4-15 in number, epipetalous, or partly also episepalous, rarely in part staminodial; Ovary mostly superior, rarely semi-inferior when immersed in the disk, or inferior when connate with the cup-like flower-axis (Schoepfia), either 1-locular with 2-3 (-5, -7) ovules pendent from the apex of a central free placenta (sometimes projecting into the stylar canal), or 3 —5 (-7)-locular in the lower part only (rarely completely so), a single ovule hanging then from the inner angle into each of the cells; Fruit a drupe with a thin and often fleshy, sometimes dehiscent or caducous exocarp, and a crustaceous to woody endocarp, or concrescent with the cup-shaped floral axis, or with an accrescent calyx or disk which then forms an external fleshy layer. Seed 1;

Distribution

Africa: present Asia-Tropical: Australasia: Central Africa: present Madagascar: present Old World: present Pacific: present Pantropical: present SE. Asia: present SW. China: present tropical America: present
A pantropical family with about 27 genera and approximately 170spp., predominantly in the tropics, a few in the subtropics.
In Malesia 9 genera with a total of 14 spp. Of these only Ochanostachys is strictly limited to Malesia. Erythropalum, Harmandia and Scorodocarpus are Indo-Malesian. Some have a wider Old World range, viz. Anacolosa (1 sp. in Central Africa, 2 spp. in Madagascar and 3 spp. in the Pacific), Olax (also in Africa, Australia, and the Pacific), and Strombosia (also in Africa). Schoepfia is Indo-Malesian, with c. 20 spp. also in tropical America. Ximenia is pantropical. The genus Malania (limited to SW. China) is closely related to Scorodocarpus.
The Malesian representatives thus show a distinct alliance with those of SE. Asia, and a less marked one with Australia and the Pacific (Anacolosa, Olax, Ximenia). Alliances are strong with Africa in the genera Anacolosa, Olax, and Strombosia.

Dispersal

Little is known of the seed dispersal of Olacaceae; their fruits with fleshy pericarp and a big seed point to a possible dispersal by animals, mainly monkeys and birds eating the fruits. Fruits of the coastal Ximenia are able to float for some time in seawater ().

Morphology

The family has an interesting morphology in that, though small in size, it exhibits pro ratio a great pluriformity in important features as compared with many other families. The habit may be erect or scandent, plants may be armed with spines or thorns (Ximenia, Olax) or unarmed; in Erythropalum axillary tendrils occur (), even rarely bifid. Of several genera it has been proved that they are hemiparasitic.

Also in the flowers variability occurs in merousness, and stamens, which are usually epipeta-lous, may also occur partly episepalous, rarely in part staminodial; stamens may be up to 3-seriate.

The ovary is superior, but may become through various ways of concrescence with disk and/or receptacle inferior or lead to an inferior fruit.

In Erythropalum flowers are bisexual or andro-dioecious, in Ximenia flowers are bisexual or rarely functionally unisexual, in Olax scandens and Schoepfia flowers are often heterostylous, in Harmandia flowers are monoecious, in many others they are normally bisexual.

The ovary is either one-celled with a central placenta or the lower part is more-celled with ovules pendent in these cells. Ovules may be bitegmic, unitegmic or even ategmic.

Phytochemically there is also variability: in Ochanostachys and Harmandia tissues contain cells with milky juice, Scorodocarpus reeks of garlic, while Erythropalum has also a bad smell.

Leaf and wood anatomy and pollen morphology are also very diverse; see below.

This pluriformity is striking, because the family must be of ancient date, as can be derived from the fact that it does not only range over the tropics of all continents but even three genera are trans-Atlantic and one trans-Pacific.

Anatomy

For general accounts see SOLEREDER (1899, 1908), METCALFE & CHALK (1950), REED (1955) and BAAS et al. (1982, with full references to older literature). Leaf and wood anatomy of the Olacaceae are very diverse, but still support the concept of a natural family. Stomatal type, secretory cavities, laticifers, silicified cells, nodal, petiole and midrib vasculature, idioblastic sclereids, type of vessel perforations, parenchyma distribution, ray type, and fibre pitting all show distinct character states enabling a reconstruction of phylogenetic trends and relationship patterns within the family (see BAAS et al., 1982; REED, 1955). Most Malesian genera have their closest relatives in Africa and/or the New World. Ochanostachys is anatomically more or less identical to Coula (Africa) and Minquartia (South America) and has both secretory cavities and laticifers. Harmandia strongly resembles Aptandra from Africa and South America and shares the occurrence of infrequent (reduced?) laticifers in the mesophyll. Anacolosa has its closest relative in the neotropical genus Cathedra. Olax, Schoepfia, and Ximenia belong to a larger, anatomically fairly homogeneous group including African and neotropical representatives. This group also shares many characters with Anacolosa and Cathedra on the one hand, and with San-talaceae and Loranthaceae on the other. Strombosia belongs to a well defined anatomical assemblage including Strombosiopsis and Diogoa from Africa and Tetrastylidium from South America. This group is unrelated to Anacolosa, with which it has been placed in the same tribe Anacoloseae in the past. Scorodocarpus shows remote affinities to Strombosia, but is closer anatomically to the neotropical Brachynema. Erythropalum remains anatomically fairly isolated within the family, but differences are insufficient to advocate a separate family. The geographical distribution of the anatomical units (largely coinciding with the traditionally recognized tribes, with the exception of the Anacoloseae) is suggestive of considerable age and conservatism of the anatomical character complexes. For a key to the genera based on leaf anatomy, see BAAS ET al. (1982). A detailed wood anatomical survey of the family is in preparation (L. VAN DEN OEVER, Blumea).— P. BAAS.

Taxonomy

The family as a whole is characterized by a free basal central placenta from which a single ovule is pendent into each of the generally imperfect cells of the ovary, or in case of a 1-celled ovary, several ovules from the apex of such a free placenta. The ovules are bitegmic, or more often unitegmic, or have — mainly in parasitic species — no integument at all. The ovary is hypogynous in principle, but may become semi-hypogynous or even epigynous by concrescence with the calyx, disk or flower-axis. The fruit is drupaceous, not rarely ± included by the accrescent calyx or disk.

Olacaceae are regarded by ENGLER (Syllabus, 1924) to represent the most primitive family of the Santalales with regard to the occurrence of hemiparasitism and the reduction in number of the integuments. ENGLER has divided the family in the first edition of ENGLER & PRANTL, Nat. Pfl. Fam. () into 3 subfamilies with 6 tribes mainly on the base of the presence or absence of integuments and the position of the micropyle on the ovulum. These subdivisions have been maintained by the author in the second edition, 16b (1935). However, the characters used by ENGLER to distinguish subfamilies were based on too scanty observations to prove the constancy needed for such high taxonomic rank as that of a subfamily.

Characters may prove more variable than assumed; for example AGARWAL () found that in Olax both unitegmic and ategmic species occur, which means that more observations in embryology are needed.

The tribes distinguished by ENGLER are mainly based on the presence or absence of starch and/or fatty constituents in the endosperm, and on the amount of fusion between the stamens. These tribes are not well established as the mentioned chemical constituents are not fully known yet in all members of the genera concerned. At the moment a subdivision of Olacaceae into natural subfamilies and tribes is still open.

Cytology

Only in the allied Santalaceae species of a fair number of genera have been examined; this yielded 2n = 20, 24, 30, 38, 40, and 72.

The two species of Olacaceae examined, one in Heisteria and one in Strombosia, yielded 2n = 38 and 40 respectively. The one species examined in Opiliaceae, viz. of Opilia, showed 2n = 20. Although the evidence is small, it does support the affinity between the three families.

Uses

Scorodocarpus borneensis provides a deep red timber (kulim). The timber of other genera (Anacolosa, Strombosia) is less important, usually of small size, and only locally used. Ximenia americana has a hard yellowish wood similar to Sandal wood, and is used locally. Young leaves of Strombosia javanica are eaten. Edible fruits are known of Scorodocarpus borneensis and Ochanostachys amentacea. The kernel of Ximenia americana contains a strong purgative.

Notes

The most important paper on Malesian Olacaceae has been written by VALETON (). In a precursor I have given an account of the genera and species of Asia, Malesia and adjacent areas (). All genera of this part of the world occur also in Malesia, with the exception of the monotypic genus Malania which is endemic in SW. China.

Phytochemo

There is a more or less general tendency in Olacaceae to deposit oxalate of lime in various parts, and silicic acid in leaves (not in wood). Seeds tend to be rich in oil. Triglycerides with C-18 acetylenic acids such as santalbic (ximenyncic), isanic and isanolic acid occur amply in seed oils (e.g. Ximenia americana), but are also present in roots, stems and leaves (Ximenia americana, Olax stricta), linking Olacaceae biochemically with Santalaceae and Opiliaceae.

The lack of knowledge about polyphenolic compounds in Olacaceae is astonishing. Tannins, probably of mixed origin (mainly flavonoid type, but sometimes accompanied by galloyl tannins) are abundantly present in the bark, roots or leaves of Ximenia americana, Anacolosa spp., Olax spp., and others.

Prunasin-like (i.e. yielding HCN and benzaldehyde) cyanogenic glycosides are present in different parts of Ximenia spp. and Olax spp. Saponins seem to occur rather widely in Olacaceae. Olacaceous sapogenins appear to be mainly triterpenoids; this character is shared with, among others, Opiliaceae and Santalaceae.

Alcaloids are possibly present in some species of the palaeotropic genera Anacolosa, Olax, and Strombosia.— R. HEGNAUER.

Embryology

Cf. .