Ericaceae (incl. Empetraceae, Monotropaceae, Pyrolaceae)
Recent phylogenetic molecular research suggests the inclusion of Empetraceae, Monotropaceae and Pyrolaceae in Ericaceae (APG III 2009). Monotropa, on the contrary, is segregated and the native species M. hypopitys now belongs to the genus Hypopitys (as H. monotropa Crantz).
An interesting overview of the cultivars of Calluna and Erica is provided by Munson (1984).
1. Herbaceous perennials without chlorophyl (lacking green pigment in all parts) (native) === Hypopitys (Monotropa s.l.)
1. Small shrubs or herbaceous perennials with chlorophyl === 2
2. Rhizomatous, herbaceous perennials with rosette of basal leaves. Petals 5, all free === 3
2. Small shrubs, without rosette of basal leaves. Petals fused at base or free (if free, only 2-3 in number) === 5
3. Flowers solitary === Moneses
3. Flowers in a raceme === 4
4. Inflorescence 1-sided. Ovary at base with 10 minute nectariferous glands === Orthilia
4. Inflorescence not 1-sided. Ovary without nectariferous glands (native) === Pyrola
5. Usually dioecious. Petals (2-)3, free at base (native) === Empetrum
5. Usually monoecious. Petals 4-5, fused at base === 6
6. Ovary inferior. Fruit a smooth berry === Vaccinium
6. Ovary superior. Fruit a capsule or a berry (in the latter case very warty) === 7
7. Petals 4 === 8
7. Petals 5 === 10
8. Leaves alternate, 3-5(-7) mm wide, white tomentose on lower surface. Corolla deciduous after anthesis. Anthers without appendages === Daboecia
8. Leaves opposite or in whorls, 1-2 mm wide, never with a conspicuous white tomentose lower surface. Corolla persistent. Anthers with or without appendages === 9
9. Sepals (petal-like!) slightly longer than petals. Flowers with calyx-like bracts at base. Leaves opposite (native) === Calluna
9. Sepals distinctly shorter than petals. Calyx-like bracts absent. Leaves verticillate, in whorls of 3 or more === Erica
10. Corolla more than 30 mm across, mauvish-purple or yellow. Leaves evergreen or deciduous, alternate === Rhododendron
10. Corolla much smaller, at most 15 mm across, pink or white. Leaves evergreen, opposite (or in whorls) or alternate === 11
11. Corolla white. Leaves with serrate margins === 12
11. Corolla pink. Leaves with entire margins === 14
12. Fruit enclosed by the fleshy, accrescent calyx. Small shrub with decumbent stems. Leaves 15-45 mm long === Gaultheria
12. Fruit not enclosed by the calyx. Shrubs or small trees with erect stems. Leaves 4-16 cm long === 13
13. Fruit a dry capsule. Inflorescence a raceme, axillary. Anthers without appendages === Leucothoe
13. Fruit a warty berry. Inflorescence a panicle, terminal. Anthers with two long appendages === Arbutus
14. Leaves alternate. Anthers each with two long terminal appendages. Shrub to 35 cm tall. Corolla pale pink, 5-8 mm across (native) === Andromeda
14. Leaves opposite or in whorls of 3. Anthers without appendages. Shrub up to 100 cm tall. Corolla reddish pink, 6-12 mm across === Kalmia
Additional alien: Ledum palustre L. (N-Am., garden escape). Gaultheria shallon Purh is also claimed as an escape from cultivation (Lambinon & al. 2004) but this requires confirmation.
References:
APG III (2009) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants. APG III. Bot. J. Linn. Soc. 161(2): 105-121.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Munson R.H. (1984) Heaths and heathers cultivated in North America (Ericaceae). Baileya 22: 101-133.