Cactus (Melocactus pachyacanthus)

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Melocactus pachyacanthus pachyacanthus with distinctive cephalium
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Cactus fact file

Cactus description

KingdomPlantae
PhylumTracheophyta
ClassMagnoliopsida
OrderCaryophyllales
FamilyCactaceae
GenusMelocactus (1)

Melocactus pachyacanthus is a squat, rounded cactus. Two subspecies are recognised which differ in the appearance of their stems; M. p. subsp. pachyacanthus has a waxy bluish-green sheen and woolly areoles, whilst M. p. subsp. viridis lacks wool and may have a waxy covering only when young (2). The stem is distinctively crowned by a concentration of dull pinkish-red bristles known as a 'cephalium', which may reach up to 30 centimetres high and 10 centimetres in diameter (2). This feature is characteristic of cacti from the genera Melocactus and Discocactus (4). The stem of the cactus has 9 to 11 low ribs, bearing rows of areoles from which stout reddish spines extend (2). Deep pink-red flowers are produced although they barely extend beyond the cephalium; following fertilisation, pale, cylindrical fruits develop (2).

Size
Height: 15 - 30 cm (2)
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Cactus biology

Hummingbirds pollinate the flowers of this cactus and the fruits are probably distributed by lizards (2).

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Cactus range

Endemic to Bahia State in eastern Brazil, this species has a restricted range within the Rio São Francisco drainage basin in the northern part of the State (2).

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Cactus habitat

Melocactus pachyacanthus inhabits the dry thorny forests region of eastern Brazil known as caatinga vegetation (2). It is usually associated with exposed limestone rocks (2).

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Cactus status

Melocactus pachyacanthus is classified as Vulnerable (VU) on the IUCN Red List (1), and is listed on Appendix II of CITES (3).

IUCN Red List species status – Vulnerable

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Cactus threats

Habitat destruction is widespread in the caatinga region of eastern Brazil; over the centuries, forests have been cleared for fuel and for the conversion of the land to agriculture (2). As a result, M. p. subsp. viridis has now been lost from all but a single site within its former range, where, as of 2003, fewer than 50 individual plants survive (2).

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Cactus conservation

International trade in wild-taken Melocactus pachyacanthus is restricted by its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) (3). The largest population of M. p. subsp. pachyacanthus numbers over 1000 individuals and is fully protected within the Gruta dos Brejoes protected area (2). The future of M. p. subsp. viridis is far from secure however, and urgent field research is needed in the hope of discovering new populations of this subspecies (2). A greater network of protected areas within the vast caatinga region is a conservation priority if its endemic species are going to persist.

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Find out more

For more information on Brazilian cacti see:

 

  • Taylor, N.P. and Zappi, D.C. (2004) Cacti of Eastern Brazil. Royal Botanic Gardens, Kew.
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Authentication

Authenticated (20/3/03) by Dr Nigel Taylor, Royal Botanic Gardens, Kew.
http://www.rbgkew.org.uk

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Glossary

Areoles
In cacti, the felted or woolly, cushion-like structures from which spines grow, flowers develop and new stems arise.
Endemic
A species or taxonomic group that is only found in one particular country or geographic area.
Fertilisation
In a flowering plant, fertilisation is the process of a pollen grain joining with the ovule (female egg cell). After fertilisation, the female parts of the flower develop into a fruit.
Subspecies
A different race of a species, which is geographically separated from other populations of that species.
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References

  1. IUCN Red List (August, 2013)
    http://www.iucnredlist.org
  2. Taylor, N.P. and Zappi, D.C. (2004) Cacti of Eastern Brazil. Royal Botanic Gardens, Kew.
  3. CITES (August, 2013)
    http://www.cites.org
  4. Hewitt, T. (1993) The Complete Book of Cacti and Succulents. Dorling Kindersley, London.
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Image credit

Melocactus pachyacanthus pachyacanthus with distinctive cephalium  
Melocactus pachyacanthus pachyacanthus with distinctive cephalium

© Nigel P. Taylor / Royal Botanic Gardens, Kew

Royal Botanic Gardens, Kew
Richmond
Surrey
TW9 3AB
United Kingdom
Tel: +44 (0) 208 332 5000
Fax: +44 (0) 208 332 5197
info@kew.org
http://www.rbgkew.org.uk

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