In this article we will discuss about:- 1. Characters of Polygonaceae 2. Distribution of Polygonaceae 3. Economic Importance 4. Affinities 5. Important Types.
Characters of Polygonaceae:
Mostly herb, climbing, leaves stipulate ochrea intrapetiolar, sheathing, swollen nodes; racemose, flowers small, crowded, di-trimerous, hypogynous, hermaphrodite, polyphyllous in two whorls; stamens 6 (3 + 3) or more; carpels (3), 1-loculed, single basal ovule; fruit a nut, enclosed by persistent membranous perianth.
A. Vegetable characters:
Mostly herbs e.g. Polygonum plebejum, annual or perennial rarely shrubs (Polygonum hydropiper) or small trees (Coccoloba uvifera); tendrills – climber (Antigonum spp.). Acidic properties due to presence of various oxalates.
Generally herbaceous with swollen nodes surrounded by a stipular sheath; sometimes bent like a knee i.e., geniculate; phylloclades in Muehlenbeckia.
Simple, alternate, sometimes sparse, entire, lobed leaves occur in Rumex acetosella; leaves usually sour in taste due to the presence of calcium oxalate crystals in the cells.
In Muehlenbeckia platyclados leaves very few or absent, the stem is modified into flat and green phylloclades; leaves radical in Rumex hastatus; stipulate, stipules form an intrapetiolar sheath, the ochrea (= ocrea) which surrounds the nodes, stipules sometimes fimbriate or hairy or rarely absent as in Koenigia islandica. The leaves may have a felt of hair as an adaptation to cold.
B. Floral characters:
Variable compound, the general plan usually is racemose but may also be a spike or a panicle; the individual bunches may be built on cymose pattern. Erigonum, which is non-ochreate, has its flowers in cymose umbels or heads.
Small, open, crowded on the inflorescence; parts arranged in 4 or 5 whorls; trimerous, rarely dimerous as in Oxyria digyna; bisexual, rarely unisexual than monoecious or dioecious; cyclic or acyclic, actinomorphic, hypogynous; honey secreted in large amount.
Tepals 3 to 6 in two indistinguishable whorls (= homochlamydeous). According to Laubengayer (1937) the trimerous whorled plan is fundamental, the apparent spiral plan is fundamentally whorled as can be seen anatomically; when 5 tepals are present, the fusion of one of the outer tepals with one inner has occurred; tepals usually pink, green or white and often persistent.
The inner tepals are sometimes enlarged as memberanous wings (Rumex) or rarely the outer ones enlarge (Triplaris) or these may get modified as hooks, spines or bristles and help in the distribution of the fruit.
Stamens 6 to 9, in two whorls, the six outer ones often introrse, the three inner extrorse (Polygonum fagopyrum), A4 in Polygonum diospyrifolium; A 4+2 in Oxyria; filaments free or slightly adnate with tepals at the base; anthers 2-celled, longitudinal dehiscence.
Generally tricarpellary, rarely bicarpellary (Oxyria and some species of Polygonum), syncarpous, unilocular, superior; ovule one, orthotropous, basal placentation, style 1, stigmas 2-4. The ovary is subtended by a nectariferous disc which may be lobed with as many as 8 lobes.
A dry nut with a single seed, it may be three-sided or biconvex, laterally winged, or an achene with wings. The wings may be furnished in bristles or hooks.
With embryo excentric or lateral, curved or straight; the endosperm mealy and copious.
Flowers made conspicuous by crowding and nectar secrereted by the disc aid in cross pollination mostly by insects (Polygonum), anemophious in Rumex, when cross pollination fails self pollination may take place.
Distribution of Polygonaceae:
It is commonly called buck-wheat or knot-wheat or smartweed family. It contains about 40 genera and 1000 species mostly distributed in the north temperate regions, a few in tropical, arctic or Southern hemisphere. In India it is represented about 10 genera and 100 species.
Economic Importance of Polygonaceae:
Coccoloba uvifera supplies edible fruits as well as gum kinos. The starchy seeds of Fagopyrum esculentum, called ‘buckwheat’, from an article of diet. The young shoots of Rumex conglomerate, R. crispus, R. obtusifolia and R. uesicarius are used as edible greens. The leaves of R. hastatus are used as condiment.
Rheum emodi is of medicinal value. The root-stock of R. officinale (China) and R. palmatum (Turkey) is the source of ‘drug rhubarb’.
Polygonum tinctorium and Rumex dentatus yield dye.
Antigonum leptopus, Coccoloba uvifera and Polygonum aubertii.
Common plants of the family:
1. Polygonum plebejum- Diffused branched prostrate herb.
2. Antigonon leptous- Railway creeper, a garden climber, bearing panicle of pink or white flowers.
3. Calligonum polygonoides L. is a slow-growing nearly leafless shrub.
4. Coccoloba uvifera L. and Muehlenbeckia platyclada Mesin are characterised by flattened leaf-like stems.
5. Polygonum barbatum L., P. glabrum L., P. orientale L. and P. serrulatum Lagasc are weeds in ditches and damp places.
6. Muehlenbeckia platyclados Meissn.; stem flattened, phylloclade like, cultivated as an ornamental.
7. Rumex maritimus L. is a marsh weed whose perianth segments have white tubercled midrib.
Division of the family and chief genera:
The Polygonaceae is divided into three subfamilies, each with two tribes:
Sub-family I. Coccoloboideae:
Tribe (i) Cocolobeae:
Flowers bisexual. Examples: Coccoloba, Muehlenbeckia, etc.
Tribe (ii) Triplarideae:
Flower unisexual. Example: Triplaris.
Sub-family II. Polygonoideae:
Flowers somewhat cyclic. Endosperm non-ruminate.
Tribe (i) Atraphaxideae:
Shrubs. Example: Calligonum.
Tribe (ii) Polygoneae:
Herbs. Examples: Fagopyrum, Polygonum etc.
Sub-family III. Rumicoideae:
Flowers cyclic. Endosperm non-ruminate.
Tribe (i). Erigoneae:
Ochreate stipules absent.
Antigonon, Erigonum, etc.
Tribe (ii). Rumiceae:
Ochreate stipules present.
Rumex, Rheum etc.
Affinities of Polygonaceae:
In Bentham and Hooker’s arrangement, the Polygonaceae is the last member of the Curvembryeae under the Monochlamydeae. Engler included the family in a distinct order (Polygonales), lying between the Aristolochiales and Centrospermae.
Bessey accepted the family as an advanced taxon of the Caryophyllales. Hallier considered its position under the Caryophyllales, seeking its origin directly from early Ranales on a line parallel to the Papaveraceae.
Rendle expressed the view that the Polygonaceae occupies a somewhat isolated position. Hutchinson opined that the Polygonales is a degraded and reduced type of the Caryophylolales, descending from the Ranales.
The Polygonaceae is related to the Amaranthaceae, Chenopodiaceae and Nyctaginaceae in the plan of floral structure, but differs from them by the presence of orchreate stipules, triangular ovary, solitary erect ovule and S-shaped embryo. The family is also allied to the Urticaeae by having stipulate leaves and orthotropous ovules.
An unique feature of the family, as suggested by Rendle, is “the multiplication of the stamens and the relation between the two-whorled trimerous and the cyclic perianth”.
Important Types of Polygonaceae:
1. Polyonum glabrum (Fig. 88.1):
An annual or perennial herb.
Tap root, Branched.
Herbaceous, weak, semi-erect, branched, cylindrical, differentiating into nodes and internodes, glabrous, green to greenish pink.
Ramal and cauline, simple, alternate, stipulate, stipule ochreate, petiolate or sub-sessile, lanceolate, entire, acute or acuminate, unicostate reticulate, large, tapering at the base.
Racemose, forming a terminal panicle.
Bracteate, ebracteolate, pedicellate, complete, hermaphrodite, actinomorphic, pentamerous, hypogynous, small, pink.
Tepals 5, polyphyllous, ovate, quincuncial, pink.
Stamens 5 to 8 or very rarely more, arranged in an outer whorl of 5 introrse stamens and inner whorl of 2 or more exstrose stamens, dithecous, basifixed, filaments long.
Tricarpellary, syncarpous, superior, unilocular, ovule one, basal placentation, style long, stigma bifid, fringed.
Endospermic with curved embryo.
2. Corculum leptopus Stuntz (Syn. Antigonon leptopus) (Fig. 88.2):
A perennial, tendril climbing herb.
Climbing, climbs by tendrils which represent modified branches (stem tendrils), ribbed, hairy, solid, cylindrical, weak, herbaceous.
Simple, cauline, petiolate, stipulate, stipules reduced to a rim like structure alternate, cordate, entire and acute or acuminate; unicostate reticulate venation.
Short cymes of three flowers arranged on long axillary inflorescence axis which continues growth and terminates above in a branched tendrils (Axillary raceme ending into a tendril).
Bracteate, pedicellate, (pedicel hairy and pink), complete, bisexual, actinomorphic, hypogynous, pink.
Tepals, 5, polyphyllous three outer ovate-cordate, two inner oblong, petaloid, pink, quincuncial aestivation.
Stamens 8, arranged in one or two whorls, polyandrous, filaments coloured, hairy, broader at the base; anthers yellow, dithecous, dorsifixed, introrse.
Tricarpellary, syncarpous, ovary superior, unilocular with a single ovule, basal placentation, a nectary is located below ovary; styles 3 curved down-wards each ending into a globose stigma, stigmas 3, capitate.
Singled seeded nut.