Ericaceae are mostly shrubs, rarely trees or undershrub’s or trailing or scrambling vines. Leaves are simple, alternate or opposite or whorled, leathery, exstipulate. Inflorescence axillary or terminal clusters or raceme or panicle or flowers solitary and axillary.
Flowers are hermaphrodite, usually actinomorphic, hypogynous or rarely epigynous. Calyx 4-7- lobed, persistent; lobes imbricate; sometimes sepals free. Corolla 4-7-lobed, funnel shaped, campanulate or urceolate, imbricate or convolute, inserted on the margin of the nectariferous disc; rarely petals free.
Stamens as many as or twice as many as the petals, inserted on the disc opposite the petals; filaments often flattened or dialated and basally coherent or connate in a tube, straight or curved; anthers 2-celled, the thecae often saccate or bulbous at base, sometimes appendaged, cells dehiscing apically by pores or slits or longitudinally; pollens are in tetrads; anthers inverted during development so as to appear introrse when mature.
Carpels usually 5, syncarpous, forming a superior or inferior 5-celled ovary, ox carpels 4-10 with as many-cells in the ovary; ovules many in each cell, anatropous or obliquely amphitropous; placentation axile; style 1, conical or filiform, rarely with as many branches as carpels; stigma capitate or lobed. Fruit a-capsule or berry or baccate; seeds small, with a small straight embryo and fleshy endosperm.
Some Rhododendron, Pieris, etc. are short trees, a few are trailing, e.g. Cassiope, while Erica form the characteristic heath. Some Vaccinium are epiphytes. In Rhododendron and Vaccinium the vegetative buds are covered by caducous scales.
Endotrophic mycorrhiza occur in the roots of all plants in this family. Leaves are very small in Cassiope, Erica, Bryanthus and Ledothamnus; these are scale-like in Cassiope, imbricating and covering the stem; in Erica, Bryanthus and Ledothamnus they are needle-like.
Epigaea has dioecious flowers. In Erica and allied genera corolla is persistent. In Rhododendron the pollen tetrads are joined by fine viscous threads. Epigaea has an expanded 5-lobed stigma. Seeds are winged in Kalmia and a few other genera. In Vaccinium and allied genera the ovary is partially or completely inferior.
Floral formula may be expressed as:
Stem-anatomy shows small solitary vessels which are semiringporous. Perforations are simple or scalariform; intervascular pitting is opposite. Wood parenchyma is absent or sparse.
Fibres are bordered pitted. Ericaceae consists of about 2000 species under 70 genera. It is widely distributed in the temperate regions of the northern and southern hemispheres and the mountains in the tropics. It is almost absent in Australia.
Rhododendron has the largest number of species, about 1200 and Erica has about 650. The plants prefer acidic soil and are absent from desert areas. The majority of the Rhododendron species are concentrated in an area that includes Yunnan province of China, N. Burma and mountainous region of E.
India, 72 species growing in the Himalayas and Naga Hills. Common Rhododendron spp- the Himalayas are R. arboreum Wall. R. campanulatum D. Don., R. falconeri Hook, f., R. Dalhousie Hook f., R. cinnabarinum Hook. f. etc. Andromeda ovalifolia, Cassiope fastigiata Wall, Gaultheria fragrantissima Hook, f., etc. are Himalayan species of this family. R. Leschenaultianum Wight, occurs in the Nilgiri Hills of S. India.
The family is divided into 4 sub-families by Drude as noted below:
I. Rhododendroideae:
Anthers without appendages; fruit septicidal capsule; seeds with loose ribbed testa, often winged.
II. Arbutoideae:
Anthers appendaged; fruit berry or loculicidal capsule; seeds triangular ovate, not winged.
III. Vaccinioideae:
Anthers usually appendaged; ovary inferior or semi-inferior; fruit berry.
IV. Ericoideae:
Anthers appendaged; fruit loculicidal capsule; seeds round, not winged,
Recently Stevens made a critical study of the family and divided the same in a slightly different manner as noted below:
I. Rhododendroideae:
Winter buds with scales; corolla caducous; stamens usually without appendage, often having fine threads among the pollen tetrads; fruit a septicidal capsule; seeds often winged.
II. Ericoideae:
No winter buds or scales, habit ericoid; corolla usually persistent; stamens usually appendaged, no threads among pollen tetrads; fruit usually a loculicidal capsule or nut; seeds not winged.
III. Vaccinioideae:
Winter buds with scales; inflorescence usually a leafless raceme or panicle; corolla caducous, urceolate; stamens usually appendaged; ovary often inferior; fruit a loculicidal capsule or drupe or berry; seeds not winged.
IV. Epigaeoideae:
Lvs. cordate; dioecious plants; stamens without appendages, anthers with longitudinal slits; stigma much expanded, 5-lobed, ovary densely pubescent; placentae double.
Ericaceae is closely related to the families Clethraceae, Epacridaceae, Empetraceae and Diapensiaceae and also to Theaceae from which family or from the order Theales the order Ericales is supposed to have been derived. The family is not economically important except the oil of winter green is obtained from species of Gaultheria, and some Vacciniums have edible berries.