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Wednesday, 26 August 2015

Biological Flora of the British Isles: Ruscus aculeatus

Biological Flora of the British Isles†
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  1. Peter A. Thomas1,* and
  2. Tarek A. Mukassabi2
Article first published online: 22 MAY 2014
DOI: 10.1111/1365-2745.12265
Issue
Journal of Ecology

Journal of Ecology

Volume 102, Issue 4, pages 1083–1100, July 2014
Article has an altmetric score of 4

Additional Information(Show All)
  1. No. 275
  2. List Vasc. Pl. Br. Isles (1992) no. 158, 35, 1
  3. †
    Nomenclature of vascular plants follows Stace (2010) and, for non-British species, Flora Europaea.

Keywords:

  • climatic limitation;
  • communities;
  • conservation;
  • diseases;
  • ecophysiology;
  • geographical and altitudinal distribution;
  • germination;
  • herbivory;
  • mycorrhiza;
  • reproductive biology;
  • soils

Summary

  1. This account presents information on all aspects of the biology of Ruscus aculeatus L. (Butcher's broom) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation.
  2. Ruscus aculeatus is a multistemmed monocotyledonous shrub with leaves functionally replaced by cladodes and photosynthetic stems. It is native to southern England primarily in dry shaded woodland and hedgerows (but widely planted elsewhere) often, but not exclusively, on base-rich soil. It is rarely abundant in any habitat, usually forming widely spread discrete clumps.
  3. Ruscus aculeatus is remarkably shade tolerant and drought resistant with low water conductance and transpiration, and water storage in the cladodes. Yet unusually for a drought-tolerant stem-photosynthetic plant, it prefers shady environments.
  4. The flowers have few if any pollinating mechanisms, low seed production and fruit/seed dispersal are largely ineffective, which may be a relict of its evolution in a tropical Tertiary climate. Population survival primarily depends upon vegetative spread from stout rhizomes, aided by the plant's general unpalatability.
  5. Over-collecting for medicinal steroidal saponins has caused some population declines, particularly in eastern Europe, but it is otherwise facing few conservation problems.

Butcher's broom. Asparagaceae. Ruscus aculeatus L. is a perennial, evergreen shrub with multiple stems arising from a creeping, thick, sympodially branched rhizome to form an oval, pyramidal bush. Stems striate, green, erect, much branched, 25–80 (100) cm. Leaves reduced to triangular scarious scales < 5 mm long and replaced functionally by rigid cladodes (1–4 × 0.4–1 cm), each arising from a leaf axil; cladodes ovate, entire, dark green and spine-pointed. Mostly dioecious but occasional hermaphrodite or female flowers have been reported on otherwise male plants which led Martínez-Pallé and Aronne (1999) to classify it as subandroecious. Male and female plants very similar in appearance (Yeo 1968). Flowers 1–2, arising from the axil of a small scarious bract in the centre of the upper surface of a cladode, each with a short pedicle. Perianth greenish-white, approximately 3 mm long, in two whorls of three segments, bearing papillae. Female flowers with a cup formed from fused stamen filaments around the superior, unilocular ovary, which has a subsessile capitate stigma. Male flowers with three stamens, filaments green or violet, fused into a tube around an undeveloped ovary. Fruit a bright red globose berry, 8–14 mm with 1–4 large seeds; seed mass 163 mg.
Ruscus has shuttled between various families including Ruscaceae (Kim et al. 2010), Convallariaceae and Liliaceae (as recorded in List Vasc. Pl. Br. Isles by Kent 1992), but is currently in the Asparagaceae (Chase, Reveal & Fay 2009; Stace 2010). The genus includes approximately 7–10 species spread throughout Europe across to Iran (Yeo 1968) including the larger ornamental R. hypoglossum introduced into Britain from south-eastern Europe. There are several ornamental varieties, including var. angustifolius Boiss. with very narrow cladodes, commonest in the eastern part of its range, and var. platyphyllus Rouy with cladodes 5 cm long and up to 2.5 cm wide (Bean 1980). There are also a number of cultivars including: ‘Lanceolatus’ only female plants with very narrow cladodes five times longer than wide (Cann 2001); ‘Wheeler's Variety’ a heavy fruiting hermaphrodite; and ‘John Redmond’ and ‘Christmas Berry’ both dwarf hermaphrodites with short intercladode lengths. A yellow-fruited form has been recorded in woods at Heckfield, Hampshire (Anon 1866).
Ruscus aculeatus is the only monocotyledonous shrub native to the British Isles. It is a slow-growing, shade-tolerant shrub that occurs naturally in dry shaded woods and hedgerows in southern England, an unusual habitat for a stem-photosynthetic plant (Farmer 1918), as such species normally grow in arid, high-light environments. However, R. aculeatus also occurs on walls and cliffs, and rocky ground near the sea. It is also naturalized in many habitats including churchyards and near habitation, either deliberately planted or as a garden escape (Preston, Pearman & Dines 2002).
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