Acanthaceae
Acanthus

Acanthus arboreus Forssk.

First published in Fl. Aegypt.-Arab.: 115 (1775)
This species is accepted
The native range of this species is SW. Arabian Peninsula. It is a shrub and grows primarily in the seasonally dry tropical biome.

Descriptions

Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592

Conservation
Predicted extinction risk: not threatened. Confidence: confident
[AERP]

Vollesen, K. (2007). Synopsis of the Species of Acanthus (Acanthaceae) in Tropical East and Northeast Africa and in Tropical Arabia. Kew Bulletin, 62(2), 233-249. Retrieved from http://www.jstor.org/stable/20443348

Type
Yemen, Al Hadiyah & Kuisma, Forsskacl 379 (lectotype C!, chosen here; isolectotype BM!). A photograph of the lectotype is at K Cheilopsis arborea (Forssk.) Nees (1847: 272).
Distribution
Endemic to the Yemen Arab Republic.
Ecology
Montane bushland, now mostly degraded or secondary, old fields on terraces, roadsides, fences, steep rock faces; 1000 - 3000 m.
Conservation
The following citation from Wood (1997: 269) really cannot be bettered: "An unmistakable species whose thistle-like leaves are a feature of large areas of the escarpment and high plateau between 1000 and 3000 m. It is at its most frequent on the escarpment between 2000 and 2800 m where it is often dominant on steep eroded slopes .. It is also found on terrace walls, field borders and in a variety of waste places and is likely to become more frequent if the terrace system breaks down. It is unpalatable to grazing animals and vain attempts are made to control its spread by burning". Despite its limited total distribution this species cannot be considered as being under any sort of threat. Least concern (LC).
Note
There are two sheets in the Forsskal Herbarium in Copenhagen (C). One sheet is numbered 379 while the other sheet, originally from the Vahl Herbarium, is un-numbered. The two are very similar and could well be from the same plant. I have chosen the numbered sheet as the lectotype. The seeds from which the above cultivated specimen was grown were said to come from Qavtya (also spelled Qantya in some of the correspondence). The exact locality of this place has never been established. As mentioned in the conservation notes above, Acanthus arboreus easily adapts to disturbed vegetation and often colonises old fields and secondary vegetation and should not have any problems in co-existing with humans in this densely populated area.
[KBu]

Sources

  • Angiosperm Extinction Risk Predictions v1

    • Angiosperm Threat Predictions
    • http://creativecommons.org/licenses/by/4.0

  • Herbarium Catalogue Specimens

    • 'The Herbarium Catalogue, Royal Botanic Gardens, Kew. Published on the Internet http://www.kew.org/herbcat [accessed on Day Month Year]'. Please enter the date on which you consulted the system.
    • Digital Image © Board of Trustees, RBG Kew http://creativecommons.org/licenses/by/3.0/

  • Kew Backbone Distributions

    • The International Plant Names Index and World Checklist of Vascular Plants 2025. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0

  • Kew Bulletin

    • Kew Bulletin
    • http://creativecommons.org/licenses/by-nc-sa/3.0

  • Kew Names and Taxonomic Backbone

    • The International Plant Names Index and World Checklist of Vascular Plants 2025. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 International Plant Names Index and World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0