General Circumscription of Ericales

Ericaceae, along with Actinidiaceae, Sarraceniaceae, Roridulaceae, Cyrillaceae, and Clethraceae are part of a larger subclade of Ericales sometimes referred as to the core Ericales (Judd et al., 2002; Soltis et al., 2005). Core Ericales are characterized by inverted anthers, a usually hollow style that emerges from an apical depression in the ovary, and endosperm with haustoria at both ends. Currently Ericales contain ca 5.9% of eudicot diversity (Magallón et al. 1999), of which one third is made up of Ericaceae alone; the other families within core Ericales are fairly small. Ericaceae are sister to the Cyrillaceae, and in turn these are sister to Clethraceae.

General Circumscription of Ericaceae

The classification of the Ericalean families has undergone many changes and the history of Ericaceae is not an exception. However, recent morphological and molecular phylogenetic analyses have brought stability to our ideas of higher-level relationships by allowing us to explicitly test our hypotheses of relationships. As a result, there is compelling evidence for a broadly defined Ericaceae that also includes Empetraceae, Epacridaceae, Monotropaceae, and Pyrolaceae (e.g., Anderberg, 1992, 1993; Judd and Kron, 1993; Kron and Chase, 1993; Kron, 1996).

The delimitation of Ericaceae was addressed through phylogenetic analysis of nr 18s, rbcl, and matk data of 16 ericads and several outgroups (Kron et al. 2002a). There, Enkianthus, a genus of shrubs and small trees in the Himalayas, S China and Japan, is resolved at the base of the tree and sister to all remaining Ericaceae. Arbutoideae are the next branch after Enkianthus, followed by Monotropoideae. Next, the tree branches in two large clades, one with Styphelioideae and Vaccinioideae as sister groups, and the second one with Cassiopoideae at the base of Ericoideae. All the relationships are well supported (bootstrap), except for Cassiopoideae as sister to remaining Ericoideae (73%).

Originally, the Empetraceae (Crowberry Family= Ericoideae p.p.) consisted of 3 genera with about 5 species, occurring in the colder parts of the Northern Hemisphere, southern South America, and the coastal plain of southeastern United States. The Epacridaceae (Epacris Family= Styphelioideae p.p.) consisted of 30 genera and 400 species, occurring primarily in Australia and New Zealand, but also reaching north to the Philippine Islands and mainland Southeastern Asia, and extending east to the Hawaiian Islands and Patagonia. The Pyrolaceae (Shinleaf Family= Monotropoideae p.p.) had 4 genera and about 45 species, occurring only in the Northern Hemisphere, and being most diverse in north temperate and boreal regions. Finally, the Monotropaceae (Indian Pipe Family= Monotropoideae p.p.) had 10 genera and 12 species, occurring mostly in temperate and boreal regions of the Northern Hemisphere, except for a couple of species in the New World and Old World Tropics; this group of plants lacks chlorophyll (the green, food producing plant pigment) and is best known for the Indian Pipe genus, Monotropa.

Today, Ericaceae (blueberries, cranberries, heaths, rhododendrons, ericas, heathers, Indians pipes) are a diverse and geographically widespread family, occurring in temperate and cool tropical regions of all continents except Antarctica, and with greatest diversity in the montane Neotropics. On a worldwide basis, many of the subgroupings within the family Ericaceae have radiated in distinct continental areas. For example, the blueberry subfamily (Vaccinioideae), with over 1200 species, is most abundant in the tropics of the New World, Malaysia, and southeastern Asia. There they usually occur as epiphytic shrubs in the cool, moist montane regions referred to as cloud forests, although a few species range into warmer tropical environments or are even present in mangroves. The largest blueberry group is the polyphyletic Vaccinium with some 500 species, scattered throughout the world, but especially in SE Asia and Malesia. The heath subfamily (Ericoideae) has undergone massive speciation process, in Africa with a proliferation of over 650 species of Erica just in the Cape region of southern Africa, and in the Sino-Himalaya region and New Guinea with Rhododendron (about 850 species, including the azaleas), an ornamental genus widely known in temperate regions.

Despite the many advances already made, the phylogenetic relationships within Ericaceae remain puzzling and challenging. Delimitation between subfamilies is not always completely satisfactory and the generic limits within many of the tribes are in need of detailed work. Specifically for the New World tropics, the ongoing phylogenetic studies of Vaccinieae, the berry producing tribe (e.g., blueberries, cranberries, “mortiños”, “agraz”), are of particular relevance as Vaccinieae represent about 80% of the genera found within the Tropical Andes (Luteyn, 2002a).

Although Vaccinieae are widely distributed (except Africa, Australia, Antarctica), they are centered in the Neotropics with 30 described genera and ca. 800 species. There, the group thrives in the humid montane habitats of Central America and the South American Andes. Preliminary phylogenetic analyses of molecular data revealed a striking disparity between generic-level phylogenetic relationships of Vaccinieae and previous classification systems, indicating that 60-80% of the genera sampled are not monophyletic (Kron et al., 2002b; Pedraza-Peñalosa, 2008a, Powell & Kron, 2003). Nevertheless, pahylogenetic analyses have not particularly focused on all neotropical Vaccinieae yet and within it, only the treatments of Disterigma s.s. (32 spp.; Pedraza-Peñalosa, 2008a, 2010a) and Satyria s.s. (8 spp.; Powell, 2005) are tree-oriented monographs. Being this a diverse group that grows in rugged areas with difficult access, today less than 20% of neotropical species have been monographed.