In this article we will discuss about:- 1. Characters of Rhamnaceae 2. Distribution of Rhamnaceae 3. Economic Importance 4. Affinities 5. Important Type.
Characters of Rhamnaceae:
Plant trees, shrubs or climbers, climbing by hooks or tendrils; leaves single, stipulate, stipules often spiny, cymose in florescences; flowers hermaphrodite, perigynous; sepals 4-5 free; petals 4-5, free; stamens opposite the concave petals; a well developed intrastaminal disc present; carpels 2-4, 2-4 locular with one basal ovule in each locule, fruit drupe or capsule seeds hard.
A. Vegetative characters:
Habit:
Shrubs or trees, often spiny and sometimes hook or tendril climbing (Gouania, Helinus) or twiner (Ventilago), rarely herbs.
Root:
Tap root deep, branched.
Stem:
Usually erect, often spinose, sometimes weak, climbing by hook tendrils or twiners.
Leaves:
Simple, alternate or opposite, entire or toothed, with 3-5 prominent basal nerves; stipules small, soon falling off, spinous and persistent.
B. Floral characters:
Inflorescence:
Mostly axillary corymbs, cymes or panicles, rarely solitary; umbellate in Helinus, flowers small and inconspicuous.
Flower:
Small, yellowish-green, regular, usually bisexual (rarely unisexual by abortion of one of the essential whorls as in Rhamnus) or polygamous (Gouania); perigynous or epigynous with generally a well-developed intra-staminal disc.
Calyx:
Sepals 5 or 4, connate, lobes valvate, usually ridged internally, basally may be united with receptacle to form a hypanthium.
Corolla:
Petals 4-5, valvate inserted in the calyx tube, free, usually clawed and hooded.
Androecium:
Stamens 4-5, tree, opposite the concave petals, often enclosed within their folds and inserted with them on the axis at or below the margin or rim of the fleshy disc, which may be entire or lobed and either fills the calyx tube or is thin and simply lines it (Rhamnus)-, anthers two-celled, versatile, dehiscing longitudinally.
Gynoecium:
Carpels 2-4; ovary sessile, superior or inferior (Helinus), viz., the degree of hypogyny, perigyny or epigyny varies greatly in different species according as the ovary is free from or united with the receptacular cup; 2-4-celled, rarely 1-celled, one erect basal anatropous ovule in each cell; style short, simple; stigma 2-4-lobed.
Fruit:
Drupe or a capsule.
Seed:
Endospermic, occasionally aril is present.
Pollination:
Entomophilous.
Floral formula:
Distribution of Rhamnaceae:
Rhamnaceae or Indian jujube family or Buckthorn family includes 58 genera and about 900 species. The plants of this family are cosmopolitan in distribution.
Economic Importance of Rhamnaceae:
1. Food:
The fruits (fresh or dry) of Zizyphus spp. (Z. jujuba syn. Z. mauratiana) Z. vulgaris, and Sageretia oppositifolia are edible.
2. Medicinal:
Rhamnus purshiana (bark) yields Cascara sagrada, a laxative; Rhamnus frangula also yields a laxative called Frangula.
3. Wood:
Krugiodendron ferzeum yields the hardest and heaviest of wood known as black iron wood. Zizyphus chloroxylon yields a valuable hard wood. Frangula alnus also yields a valuable timber.
4. Dye:
Green and yellow coloured dyes are obtained from Rhamnus infectoria, R. chlorophora and Ventilago spp. The dyes are useful for colouring silk goods.
5. Cordage:
The bark of Ventilago denticulata is used for making cordage.
6. Charcoal:
Gun powder (Dog-wood) is prepared from the wood of Zizyphus mauritiana and also of Rhamnus and Frangula.
7. Ornamentals:
Species of Ceanothus, Reynosia, Noltea, Collectia, Discaria etc. are grown for decorative purposes.
Affinities of Rhamnaceae:
Bentham-Hooker’s placed Rhamnaceae under the Celastrales after the Geraniales and before the Sapindales. Rhamnaceae and Vitaceae are closely related families forming the natural series Rhamnales; the common scandent and climbing habit occur in both the families.
Perigynous structure with the reduction of one of the perianth whorls together with tendency of unisexuality and disc formation are also striking features.
The order Rhamnales including two families Vitaceae and Rhamnaceae was included in the order Celastrales by Bessey as Celastrales is closely allied to Rhamnales. Both Hallier and Bessey support the origin of Rhamnales and Celastrales from Rosales.
According to Rendle both Rhamnales and Celastrales probably had parallel origin from diplostemonous order resembling Rutales. Hutchinson (1959) put both Celastrales and Rhamnales in Lignosae near to each other, he traced the origin of Celastrales and Rhamnales as parallel series from Euphorbiales.
Common plants of the family:
1. Gouania tiliaefolia is a climber with inferior three-winged fruits.
2. Helinus lanceolatus is a cirrhose scandent shrub.
3. Ventilago denticulata is a strong climber.
4. Sageretia oppositifolia (H. Goata) – A climbing shrub, fruit small, black sweetish edible, wood is hard grained.
5. Zizyphus mauritiana (syn. Z. jujuba) ‘Ber’ – Shrub or a small spiny tree, fruit edible; bark used for tanning, the tree serves as host to lac insects.
6. Zizyphus nummularia “Jharber”, fruit is edible.
Important Type of Rhamnaceae:
1. Zizyphus mauritiana (H. Ber) (Fig. 47.1):
Habit:
A shrub or a small tree.
Root:
Tap, branched.
Stem:
Erect, branched, aerial, spinose.
Leaf:
Simple, alternate, stipulate, stipules thorny, entire or serrulate, ovate or ovate-oblong, obtuse, tomentose below.
Inflorescence:
Condensed axillary cymes.
Flower:
Bracteate, hermaphrodite, complete, actinomorphic, cyclic, hypogynous.
Calyx:
Sepals five, polysepalous, pubescent, valvate.
Corolla:
Petals five, polypetalous, small, concave, pubescent, white, valvate.
Androecium:
Stamens five, opposite the petals, filaments long, curved, anthers small basifixed, a ten lobed intrastaminal disc present.
Gynoecium:
Bicarpellary, syncarpous, bilocular, superior, ovary sunk into the disc, ovule one per locule, basal placentation, styles two, each terminating into a rough, discoid stigma, 2-fid.
Floral formula:
