Tacca
Description
Terrestrial, erect, perennial, mostly rosulate, scapose herbs.
Leaves up to 13, appearing together with the inflorescence, either spaced or crowded on the rhizome, petioled, entire, pinnatifid, palmatipartite or palmatisect and palmatisect with pinnately divided segments;
Inflorescences umbellate, involucrate, sometimes bracteate;
Flowers actinomorphic, bisexual, epigynous, gamophyllous, with 6 lobes in 2 whorls, imbricate in bud, mostly very dark coloured, parallel- or curvinerved;
Stamens 6, inserted on the corolla tube, epitepalous, outer ones slightly larger than inner ones;
Ovary 1-celled, 3-carpellate, obpyramidal, 6-ribbed;
Fruits berry-like, with a fleshy pericarp, 6-ribbed, irregularly desintegrating, rarely (in one extra-Mal. sp.) dehiscent.
Seeds completely filling the fruit, l0-∞. with a strongly ribbed, mostly glabrous testa and a mostly distinct raphe.
Distribution
Asia-Tropical, Old World present, pantropical, within the tropics of Cancer and Capricorn present, tropical South America present
Ten species, pantropical, within the tropics of Cancer and Capricorn, mainly developed in Malesia, where 8 out of 9 Old World species occur; 1 species in tropical South America. .
Dispersal
The ovoid or reniform, albuminous, ribbed or papillate seeds are smallish (c. 4-8 mm), with a fairly hard testa; they are freed in that the limping, decumbent, fruiting peduncle sags and deposits the fruit on the soil where it disintegrates; only in the continental SE. Asian species T. plantaginea the scape remains obvious erect and seeds are shed from a capsular fruit. How these seeds are dispersed over larger distances is unknown, but the more or less fleshy fruits will probably be eaten by ground animals; the raphe of the seed is distinct and fleshy. Some seeds must lead to new specimens at close range as Taccas are mostly found in groups of specimens.
In T. leontopetaloides the tuber emits from the growth apex thickish runners which grow downward and form a new tuber at apex, replacing the original tuber.
In T. leontopetaloides the tuber emits from the growth apex thickish runners which grow downward and form a new tuber at apex, replacing the original tuber.
Morphology
The starchy, roundish or elongate, tuberous rhizomes are all naked and cauligenous. There are three types, viz a vertical elongate rhizome with apical growth in T. integrifolia, T. plantaginea (continental SE. Asia), and T. chantrieri (in T. bibracteata still unknown), a roundish rhizome with an apical cavity in T. leontopetaloides, T. palmata, and T. ebeltajae, and a horizontal elongate rhizome from the upper part of which leaves and inflorescences are emitted in a spaced way, hence without apical growth, in T. palmatifida, T. celebica, and T. parkeri (South America).
The erect peduncle (scape) terminates in an involucrum consisting of leafy, herbaceous, mostly erect bracts, between which the umbellately arranged flowers are situated. EICHLER'S assumption that the flowers are placed in cincinni must be checked anatomically. Except in the palmately-leaved species and in T. parkeri long, filiform, drooping bracts are found between the flowers.
The epitepalous stamens have a characteristic structure: the short flattened filaments are adnate to the perianth tube except for the inflexed margins and a short free apical part which is like a helmet at the inside of which the anther cells are placed.
At the base of the style an annular zone or disk is sometimes present; in this zone glandular cells are present together with short or long emergences. Only in T. leontopetaloides the disk is clearly developed and provided with glandular hairs.
The erect peduncle (scape) terminates in an involucrum consisting of leafy, herbaceous, mostly erect bracts, between which the umbellately arranged flowers are situated. EICHLER'S assumption that the flowers are placed in cincinni must be checked anatomically. Except in the palmately-leaved species and in T. parkeri long, filiform, drooping bracts are found between the flowers.
The epitepalous stamens have a characteristic structure: the short flattened filaments are adnate to the perianth tube except for the inflexed margins and a short free apical part which is like a helmet at the inside of which the anther cells are placed.
At the base of the style an annular zone or disk is sometimes present; in this zone glandular cells are present together with short or long emergences. Only in T. leontopetaloides the disk is clearly developed and provided with glandular hairs.
Taxonomy
PAX (1887) and LIMPRICHT (1928) subdivided the genus into two and three sections respectively, mainly based on the degree of dissection of the leaves and presence cq. absence of the filiform bracts. These sections are in my opinion unsatisfactory from the affinity point of view; there are four or five groups of species, three of which monospecific, and I find it undesirable to give these formal sectional rank. The only New World species, T. parkeri SEEM., occupies a rather isolated position, in that it does not fit into any of the Old World groups but shares certain characteristic characters with all of them.
Uses
The only species that is a useful plant for its edible tubers is T. leontopetaloides; see there.
Phytochemo
Starch is (or was) produced from the tuberous rhizomes of several species of Tacca. The underground parts are reported to be bitter and toxic; special treatments are used to make edible the starch or whole tubers. Unfortunately the chemical nature of the constituents of Taccaceae is still completely unknown. Alkaloids are said to be present in T. integrifolia KER-GAWL. (syn. T. cristata JACK) and T. leontopetaloides (L.) O.K. The tubers of the latter species were investigated by J. SCHEUER et al. (). Besides ubiquitous substances like sucrose, β-sitosterol and cerylic alcohol, a bitter principle and a yellow ester were isolated by these authors. Preliminary investigations of the bitter principle, named taccalin, indicate that it represents a rather unusual plant constituent. No structures of the systematically more relevant constituents of Taccaceae being known at present, chemotaxonomy cannot yet give any help to plant systematics in this instance. — R. HEGNAUER.