Violaceae

Primary tabs

Violaceae

Description

Shrubs, small trees, or lianas, in Malesia evergreen, or herbs. Leaves in Malesia spirally arranged, sometimes distichous, simple, the margin often shallowly incised; Stipules present. Inflorescences axillary variously modified bundles, or racemes, or panicles, sometimes terminal, or flowers solitary in the leaf axils; Flowers bisexual or rarely dioecious, actinomorphic or zygomorphic, particularly in the corolla; Sepals 5, the median one adaxial (posterior), free or occasionally for a small portion connate, often ciliate. Petals 5, free, generally sessile, the median one abaxial (anterior), often longer and differently shaped, the base then mostly with a sac or spur. Fruit in Malesia capsular, the carpels thickened to boat-shaped leathery or woody valves (in the latter eventually the endocarp separated from the pericarp) which spread and often compress upon dehiscence. Seeds 1-many, sessile, one to a few mm in size, often with distinct raphe, sometimes with funicular outgrowths;

Distribution

America: present Asia-Tropical: New Zealand: present Pantropical: present Polynesia: present SE. Australia: present subtropics: present
A pantropical family; only Viola is cold-loving. Hybanthus extends into the subtropics, so does Melicytus () in Polynesia and New Zealand. Hymenanthera (congeneric with the former? ) is temperate in SE. Australia and New Zealand. Number of genera 16, 8 of them from America; the largest are Viola, currently credited with c. 400 spp., Rinorea with c. 200, Hybanthus with perhaps 70, and there are about 50 more in the other genera altogether. Total number of species c. 720, in Malesia 31, two of these introduced.

Notes

BENTHAM & HOOKER’S subdivision of the family () was extended and modified by ; for an account in English of the latter’s phylogenetic considerations, see .
Dr. D. M. MOORE'S contribution consists of the genus Viola; he also checked the family description.
Indexes to the examined specimens were published in the series ‘Identification Lists of Malaysian Specimens’, and .

Phytochemo

Accurate chemical information about Violaceae is scanty notwithstanding the fact that members of this family are used in popular medicine all over the world. The present summary of chemical characters, therefore, must be considered as a very preliminary one. Different types of crystals of oxalate of lime occur commonly. Members of the genera Amphirrhox and Allexis accumulate aluminium according to CHENEREY (). Leaves and flowers contain rather large amounts of acidic mucilage in many instances; usually the mucilage is present in epidermal cells. In some taxa cells with a yellow or reddish ‘resin-like’ content replace mucilage cells; these latter cells also occur in the mesophyll and in the cortex, phloem and pith of stems. The chemical nature of the content of these idioblasts is not known. However, the fact that leucoanthocyanins are rather widespread in Violaceae suggests that the yellow to reddish cell contents may represent so-called ‘myriophyllin’ or ‘incluses’. Personal observation on rhizomes of Viola mirabilis L. confirm this supposition. According to PECKOLT () fresh leaves of Leonia glycycarpa R. & P. are used for the preparation of a bird-lime in Brazil; this suggests that at least some members of the family may have rubber-containing idioblasts. Roots of several species of Hybanthus (= Ionidium) store inulin-like fructans instead of starch; other Violaceae store essentially sugars or starch ().
Preliminary observations about polyphenols constituents of leaves () showed a wide range of compounds; leucoanthocyanins, flavonol and flavones may be present in various combination; ellagic acid, however, was observed only in trace amount in three species of Viola. Saponins seem to be rather common in violaceous plants; they have been demonstrated to be present in many species of Viola and in some species of Hymenanthera, Hybanthus, and Melicytus; none of the saponins has been investigated chemically hitherto.
There is much confusion about alkaloids in literature; roots and rhizomes of species of Hybanthus and of Viola odorata L., and other species of Viola were used formerly as a substitute for ipecacuanha root. Some authors claimed to have detected emetin or emetin-like compounds (e.g. viola-emetin; violin) in such crude drugs. Other authors, however, could not find emetin though some of them isolated minor amounts of alkaloids (e.g. anchietin, ionidin; compare ). Most probably many Violaceae contain small amounts of alkaloids; species of Anchieta, Hybanthus, Hymenanthera, Rinorea, and Viola are listed in literature as alkaloid-bearing plants; however, the structures of violaceous alkaloids are totally unknown at present.
Most chemical work has been performed with European species of Viola. Glycosides of delphinidin and cyanidin occur constantly in blue and purple flowers; violanin is a delphinidin-derived anthocyanin acylated by p-cumaric acid. Rutin occurs in flowers and in leaves of several species of Viola. From the herb of Viola tricolor L. HORHAMMER C.S. () isolated apigenin-6,8-di-C-glucoside, which was called violanthin. The flavone glycoside linarin is the main flavonoid constituent of leaves of Viola papilionacea PURSH ().
Violatoside is an arabinoglucoside of methyl salicylate; it occurs in species of the section Melanium but seems to be lacking in other sections of Viola (). From roots and rhizomes of Viola odorata L. PAILER and NOVOTNY () isolated 0.01-0.02 % of nitropropionic acid.
Concluding this survey it must be stated that a thorough chemotaxonomic discussion of Violaceae is not yet possible. At present no chemical characters are known which contradict the generally accepted relationships between Flacourtiaceae and Violaceae. — R. HEGNAUER.