Illustrations of Indian Botany, Vol. 1/Oxalideae

by Robert Wight

XLV.-OXALIDEAE.

This is the last of the Indian group of families which appertain to the class Geranioidecr, a group the members of which, when superficially viewed, seem to be most heterogynious and ill assorted, but which, when more closely scrutinized are found connected in so many import- ant points and to glide into each other by such insensible gradations, that it becomes difficult to find good ordinal characters by which to keep them distinct. The whole are marked by the predominance of the quinary proportion of parts, 5 sepals and petals ; 5-10 rarely 15, usually monadelphous, stamens ; 5 styles, and 5 cells to the ovary, with usually few superposed ovules ; 5 membranaceous 2-valved carpels, cohering round a central persistent column ;exarillate, and with the exception of Oxalidece, exalbuminous seed. Thus intimately united, the ordinal char- acters are taken from peculiarities of less importance, but yet of so obvious a character that it seems well to preserve the distinctions which have been introduced and found useful in practice.

This order though abounding in species has but few (3) genera, and these, with the excep- tion of Oxalis have exceedingly few species, J 54, out of 158 enumerated by DeCandolle in the order, belonging to that genus. Some additions have since been made but I believe very few. They most abound in America and the Cape of Good Hope. -In India the species are few, but present a great contrast in their forms — two out of about 6 or 8 Indian species being considerable trees, while all the rest are small herbaceous plants, mere weeds.

" Sepals 5, equal, sometimes cohering at the base, persistent ; aestivation imbricative. Petals 5, hypogynous, equal, unguiculate : aestivation twisted. Slamens 10, hypogynous, more or less monadelphous : those opposite the petals longer than the others : anthers erect, bilo- cular. Ovarium 5-angled, 5-celled: ovules solitary, or several in each cell : styles 5, filiform : stigmas capitate, or slightly bifid. Placentae in the axis. Fruit rarely baccate : usually cap- sular, membranous, 5-celled, and 5-10 valved. Seeds 1, or several in each cell: testa fleshy,

bursting elastically. Albumen between cartilaginous and fleshy. Embryo straight, as long as the albumen: radicle long; next the hilum : cotyledons foliaceous.—Leaves compound (or by abortion simple), alternate, seldom opposite or whorled."

Affinities. The affinity of this with the three preceding orders, has been already adverted to. Formerly it was united with Geraniaceae, and is still considered by some not sufficiently distinct. DeCandolle however thinks it more nearly allied to Zygophylleae, though quite distinct. Its compound leaves and albuminous seed in both of which respects it differs from Geraniaceae but associates with Zygophylleae, seem to confirm this view.

Geographical Distribution. The genus Oxalis is principally confined to the Cape of Good Hope and America, but is also though sparingly met with in Europe, Asia, and New Holland. The genus Averhoa is confined to India and the adjoining islands : of Biophytum one species is found in the West Indies and the rest in India.

Properties and Uses. Acidity is the predominating quality of this order. The Oxalis acetosella or wood sorrel, is well known in Europe, and esteemed on account of its cooling and refreshing properties, the expressed juice of which furnishes, when crystalized, the so-called essential salt of Lemons, or binoxalate of potash. Both species of Averhoa, namely, A. Carambola and A. Bilimbi, are equally well known on account of their intense acidity. The kind of acid which imparts the taste I have never seen mentioned, but presume it is oxalic, the one which predominates in the family. The fruit of the former is considered cooling and aperient.

Remarks on Genera and Species. Originally two genera only were referred to this family, Oxalis and Averhoa. The former of these DeCandolle split into two, more perhaps, on account of the marked difference of habit than from any well marked differences of structure. The principal points of difference consist in the filaments, being free to the base in the one (Biophytum) while they are united into a tube nearly half their length in the other (Oxalis). They also differ in the form of their fruit, the former having its capsules approaching to globose, while in the latter they are cylindrical. These distinctions, added to the very marked difference of habit have induced me to revert to DeCandolle's division, from which we departed in the Prodromus The species of the genus Biophytum are of difficult discrimination, and it has been doubted whether there are more than one in India—on this point I now feel quite satisfied, and think we may certainly acknowledge two, I think several species. Supposing we fix upon the formei number there can be no difficulty in distinguishing them, the one being marked by having a single terminal tuft of leaves on a more or less elongated simple unbranched palm-like stem—the other, by having a diffuse ramous proliferous stem, each branch terminating in a tuft of leaves. The various forms might then be ranged under these, as so many varieties. The difference of habit and station which some of these forms affect seem to stand in opposition to this extent of simplification, for example—Biophytum sensitivum is only found on the plains usually in very open ground exposed to the full blaze of the sun's light, whereas, the form figured in plate 62 is only found in cool alpine situations under the shade of thick jungles, both here and in Ceylon. These circumstances may induce the belief that the plant is the same, only altered by local circumstances, an opinion which, if urged, 1 confess I have not the means of controverting, since it can only be set aside by making the two plants change places, and in that way determining whether or not their forms would alter also. The B. sensitivum is further distinguished by being glabrous, while the other is very generally clothed with hairs, sometimes, especially on the rachis of the leaves and peduncles, very densely. This character, however, is not sufficiently constant in either form to admit of much weight being attached to it. Of the palm-like forms there are again two varieties distinguishable by the form of their leaflets—the form fig. 8 in plate 62 represents the one, that of fig. 10 nearly corresponds with the other, though not taken from it— fig. 8 is a slightly magnified leaflet of B. Candolianum—fig. 10 is that of a species to be afterwards mentioned, but, with the exception of its being a little more tapering and less distinctly mucronate at the point, gives a pretty good idea of the form of Dr. Arnott's B. (Oxalis) nudum, and will assist in distinguishing these two perhaps too nearly allied species.

Of the proliferous division, the forms are more numerous and less easily distinguished, but may perhaps be reduced to three, distinguished by the form and relative number of leaflets — 1st. B. (Oxalis) proliferwn (Arn.) leaves and leaflets small, 8- 14 pairs, rachis (mid-rib of the whole leaf) about 1 inch or 1| inch in length — Ceylon, in woods — 2d. B. intermedium (R. W.) leaflets much larger, 14-20 pairs : rachis from 2 to 4 inches long. — Ceylon aid Courlallum, shadtj woods. The leaflets of this are as large as those of B. Candolianum — 3d. B. polyphyllum (Mun : MSS.) leaflets from 30 to 40 pairs, minute, attenuated towards the apex, bristle pointed, (tab. 62, fis?. 10) rachis from 2 to 3 inches in length. — Neilgfierries — Messrs. Munro and Gough. There is yet a fourth form of this division, which may be called B. vprticeltatum, in which the tufts of leaves in place of terminating the branches form verticels round the very diffuse slender stems. — Courtallum in very dense thickets. The foliage of this form is intermediate between B. polyphyllum and intermedium, having the small obliquely pointed hairy leaflets of the former, and the smaller number of pairs, 20 to 30, of the latter.

Of these different forms I shall make it my endeavour to publish figures in my Icones, leaving the question whether they are species or varieties still undecided for future observers to investigate.

EXPLANATION OF PLATE 62.

1. Byophitum Candolianum, (R. W.) natural size.

2. Calyx, ovary, styles and stamens.

3. Corolla, the petals partially cohering.

4. Shorter stamens, back and front views.

5. One of the longer stamens with its attached scale.

6. Ovary divided vertically.

7. - - transversely, 5-celled.

8. Leaflets of B. Candolianum.

9. - - B. sensitivum.

10. - - B. polyphyllum.

OXALIDEÆ

BIOPHYTUM CANDOLIANUM. (R.W.)