Empetreae |
| The tribe comprises three genera, Ceratiola, Corema, and Empetrum. Samuelsson
(1913) was the first to show that the Empetreae were closely related to
the Ericaceae, and later Anderberg (1993), Judd & Kron (1993), and
Kron & Chase (1993) demonstrated them to be nested within the Ericaceae.
Prior to Samuelsson’s (1913) investigation the relationships of empetrids
to other plants were unclear with various proposed systematic positions,
e.g., in the orders Euphorbiales (Don, 1827), Sapindales (Pax, 1891) or
Celastrales (Hutchinson, 1969). A position as a section of Conifers was
put forward early in the 19th century (Nuttall, 1818). In recent years,
most authors (e. g., Cronquist, 1981, Takhtajan 1997) have placed empetrids
close to the Ericaceae, albeit as a separate family. Empetreae are easily diagnosed because this clade has numerous distinctive apomorphic characters, most relating to a shift from insect to wind pollination. Unlike most Ericaceae, Empetreae exhibit a high degree of dioecy (found elsewhere in Ericaceae only in Epigaea and possibly some Gaultherieae). Unique (or nearly unique) synapomorphies of Empetreae include imperfect flowers (char. #32, evolving independently in Epigaea), flowers with persistent tepals (chars. #39, 48; although persistent corollas are found in most Ericeae), stigma flabellate to pinnatifid (char. #70), and drupaceous fruits (char. #77, 81, occurring elsewhere only in Arbutoideae, some Styphelioideae, and some Vaccinioideae). Additional, more homoplasious synapomorphies of Empetreae are their lack of multicellular hairs on the leaves (char. #21), flowers with separate perianth parts (char. #44), stamens less than two times the number of petals (char. #51; see Fig. 21), and indehiscent (fleshy) fruits (char #78). In many (but not all) of the most parsimonious trees resulting from the combined morphology, matK, and rbcL analysis, the Empetreae and Ericeae form a clade, which is supported by the absence of bud scales (char. #9, also in some Phyllodoceae, Diplarche, Ledothamnus, Cassiope, and Harrimanella) and smooth filaments (char. #55, also quite homoplasious). In addition, the presence of 4-(or 2-) merous flowers may be synapomorphic, but this feature is also homoplasious. Both Empetreae and Ericeae have ericoid leaves (char. #13). However, it is noteworthy that the occurrence of gossypetin (char. #87) links Empetreae with Rhodoreae. Although the data strongly indicate that Empetreae are derived from within Ericoideae, the exact relationships to the other tribes are not fully understood. In the analysis of morphological data set (Fig. 3) Empetreae are placed in the same clade as Erica and Calluna but the support for this is very low. The matK data (Fig. 4) indicate a position for the Empetreae as sister to the Rhodoreae, but again with low support. In the combined analysis of morphological and molecular data sets, the position of Empetreae remains unresolved in relation to the Bejarieae, Ericeae, Rhodoreae and Phyllodoceae. Relationships among the genera and species of Empetreae have been studied by Anderberg (1994b). |
Empetreae |
| Empetreae D. Don, Edinburgh New Phil. J. 1827: 59. 1827. – Type
genus: Empetrum L. Coremateae Pax in Engl. & Prantl, Nat. Pflanzenfam. III, 5: 126. 1891. Shrubs, or shrublets, sometimes mat-forming, evergreen with alternate or almost verticillate, ericoid leaves, revolute in bud; leaf epidermal cells not lignified. Inflorescence axillary with solitary flowers, few-flowered clusters, or in terminal heads; bracts and bracteoles various; perianth not articulated with the pedicel. Flowers actinomorphic, reduced, choripetalous, wind-pollinated, unisexual or bisexual. Sepals and petals three to six, inconspicuous, more or less undifferentiated. Stamens 2 or 3, exserted, the filaments straight and smooth, anthers ± smooth, lacking appendages, without fibrous endothecium, dehiscing by longitudinal slits. Pollen without viscin threads. Ovary 2 to many locular, with axile placentation, superior, style short, impressed, stigma lobes deeply divided. Fruit a dry or fleshy drupe with two to many pyrenes; seeds with ± isodiametric testa cells; embryo with 2 cotyledons. |