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 berry === Vaccinium
6. Ovary superior. Fruit a capsule === 7
7. Leaves needle-like, 1-2 mm wide. Petals 4. Corolla persistent after anthesis === 8
7. Leaves never needle-like, always wider. Petals 5. Corolla caducous === 9
8. Sepals (petal-like!) slightly longer than petals. Flowers with calyx-like bracts at base. Leaves opposite (native) === Calluna
8. Sepals distinctly shorter than petals. Calyx-like bracts absent. Leaves verticillate, in whorls of 3 or more === Erica
9. Corolla more than 30 mm across, mauvish-purple or yellow. Leaves evergreen or deciduous, alternate === Rhododendron
9. Corolla much smaller, at most 15 mm across, pink or white. Leaves evergreen, opposite (or in whorls) or alternate === 10
10. Corolla white. Leaves 5-16 cm long with sharply serrate margins === Leucothoe
10. Corolla pink. Leaves up to 5 cm long with entire margins === 11
11. Leaves alternate. Anthers each with two long terminal appendages. Shrub to 35 cm tall. Corolla pale pink, 5-8 mm across (native) === Andromeda
11. 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 aliens: Gaultheria procumbens L. (N-Am., garden escape) and 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.