Ericaceae

The Ericaceae are a family of flowering plants, commonly known as the heath or heather family, found most commonly in acid and infertile growing conditions. The family is large, with roughly 4000 species spread across 126 genera, making it the 14th-most-speciose family of flowering plants.[2] The many well-known and economically important members of the Ericaceae include the cranberry, blueberry, huckleberry, rhododendron (including azaleas), and various common heaths and heathers (Erica, Cassiope, Daboecia, and Calluna for example).[3]

Description

The Ericaceae contain a morphologically diverse range of taxa, including herbs, dwarf shrubs, shrubs, and trees. Their leaves are usually alternate or whorled, simple and without stipules. Their flowers are hermaphrodite and show considerable variability. The petals are often fused (sympetalous) with shapes ranging from narrowly tubular to funnelform or widely bowl-shaped. The corollas are usually radially symmetrical (actinomorphic), but many flowers of the genus Rhododendron are somewhat bilaterally symmetrical (zygomorphic).[4]

Taxonomy

Adanson used the term Vaccinia to describe a similar family, but Jussieu first used the term Ericaceae. The name comes from the type genus Erica, which appears to be derived from the Greek word ereike. The exact meaning is difficult to interpret, but some sources show it as meaning 'heather'. The name may have been used informally to refer to the plants before Linnaean times, and simply been formalised when Linnaeus described Erica in 1753, and then again when Jussieu described the Ericaceae in 1789.[5]

Historically, the Ericaceae included both subfamilies and tribes. In 1971, Stevens, who outlined the history from 1876 and in some instances 1839, recognised six subfamilies (Rhododendroideae, Ericoideae, Vaccinioideae, Pyroloideae, Monotropoideae, and Wittsteinioideae), and further subdivided four of the subfamilies into tribes, the Rhododendroideae having seven tribes (Bejarieae, Rhodoreae, Cladothamneae, Epigaeae, Phyllodoceae, and Diplarcheae).[6] Within tribe Rhodoreae, five genera were described, Rhododendron L. (including Azalea L. pro parte), Therorhodion Small, Ledum L., Tsusiophyllum Max., Menziesia J. E. Smith, that were eventually transferred into Rhododendron, along with Diplarche from the monogeneric tribe Diplarcheae.[7]

In 2002, systematic research resulted in the inclusion of the formerly recognised families Empetraceae, Epacridaceae, Monotropaceae, Prionotaceae, and Pyrolaceae into the Ericaceae based on a combination of molecular, morphological, anatomical, and embryological data, analysed within a phylogenetic framework.[8] The move significantly increased the morphological and geographical range found within the group. One possible classification of the resulting family includes 9 subfamilies, 126 genera, and about 4000 species:[2]

Genera

See the full list at List of Ericaceae genera.

Distribution and ecology

The Ericaceae have a nearly worldwide distribution. They are absent from continental Antarctica, parts of the high Arctic, central Greenland, northern and central Australia, and much of the lowland tropics and neotropics.[2]

The family is largely composed of plants that can tolerate acidic, infertile conditions. Like other stress-tolerant plants, many Ericaceae have mycorrhizal fungi to assist with extracting nutrients from infertile soils, as well as evergreen foliage to conserve absorbed nutrients.[9] This trait is not found in the Clethraceae and Cyrillaceae, the two families most closely related to the Ericaceae. Most Ericaceae (excluding the Monotropoideae, and some Styphelioideae) form a distinctive accumulation of mycorrhizae, in which fungi grow in and around the roots and provide the plant with nutrients.[10] The Pyroloideae are mixotrophic and gain sugars from the mycorrhizae, as well as nutrients.[11]

In many parts of the world, a "heath" or "heathland" is an environment characterised by an open dwarf-shrub community found on low-quality acidic soils, generally dominated by plants in the Ericaceae. A common example is Erica tetralix. This plant family is also typical of peat bogs and blanket bogs; examples include Rhododendron groenlandicum and Kalmia polifolia. In eastern North America, members of this family often grow in association with an oak canopy, in a habitat known as an oak-heath forest.[12]

Some evidence suggests eutrophic rainwater can convert ericoid heaths with species such as Erica tetralix to grasslands.[13] Nitrogen is particularly suspect in this regard, and may be causing measurable changes to the distribution and abundance of some ericaceous species.

Use in alternative medicine

Heather has been listed as one of the 38 plants used to prepare Bach flower remedies,[14] a kind of alternative medicine promoted for its effect on health. However, according to Cancer Research UK, "there is no scientific evidence to prove that flower remedies can control, cure, or prevent any type of disease, including cancer".[15]

References

  1. ↑ Angiosperm Phylogeny Group III (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III". Botanical Journal of the Linnean Society 161 (2): 105–121. doi:10.1111/j.1095-8339.2009.00996.x.
  2. 1 2 3 Stevens, P.F. (2001 onwards). "Ericaceae". Angiosperm Phylogeny Website. Retrieved 29 December 2014.
  3. ↑ Kron, Kathleen A.; Powell, E. Ann & Luteyn, J.L. (2002). "Phylogenetic relationships within the blueberry tribe (Vaccinieae, Ericaceae) based on sequence data from MATK and nuclear ribosomal ITS regions, with comments on the placement of Satyria". American Journal of Botany 89 (2): 327–336. doi:10.3732/ajb.89.2.327. PMID 21669741.
  4. ↑ Watson, L. & Dallwitz, M.J. (19 August 2014). "Ericaceae Juss.". The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Retrieved 30 December 2014.
  5. ↑ Jussieu, A.-L. de (1789). Genera plantarum ordines naturales disposita. Paris: Herissant & Barrois. pp. 159–160.
  6. ↑ Stevens (1971).
  7. ↑ Craven, L.A. (April 2011). "Diplarche and Menziesia transferred to Rhododendron (Ericaceae)". Blumea 56 (1): 33–35. doi:10.3767/000651911X568594.
  8. ↑ Kron, K.A.; Judd, W.S.; Stevens, P.F.; Crayn, D.M.; Anderberg, A.A.; Gadek, P.A.; Quinn, C.J. & Luteyn, J.L. (2002). "Phylogenetic Classification of Ericaceae: Molecular and Morphological Evidence". The Botanical Review 68 (3): 335–423. doi:10.1663/0006-8101(2002)068[0335:pcoema]2.0.co;2.
  9. ↑ Keddy, P.A. (2007). Plants and Vegetation: Origins, Processes, Consequences. Cambridge University Press.
  10. ↑ Cairney, J.W.G.; Meharg, A.A. (2003). "Ericoid mycorrhiza: a partnership that exploits harsh edaphic conditions". European Journal of Soil Science 54 (4): 735–740. doi:10.1046/j.1351-0754.2003.0555.x.
  11. ↑ Liu, Z.; Wang, Z.; Zhou, J. & Peng, H. (2010). "Phylogeny of Pyroleae (Ericaceae): implications for character evolution". Journal of plant research 124 (3): 325–337. doi:10.1007/s10265-010-0376-8. PMID 20862511.
  12. ↑ "The Natural Communities of Virginia Classification of Ecological Community Groups (Version 2.6)". Virginia Department of Conservation and Recreation. July 2013. Retrieved 30 December 2014.
  13. ↑ Keddy, P.A. (2010). Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press. pp. 103–104.
  14. ↑ Vohra, D.S. (1 June 2004). Bach Flower Remedies: A Comprehensive Study. B. Jain. p. 3. ISBN 978-81-7021-271-3. Retrieved 2 September 2013.
  15. ↑ "Flower remedies". Cancer Research UK. Retrieved September 2013.

Bibliography

External links

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