Neotropical Aizoaceae

Nigel Taylor & Daniela Zappi

Royal Botanic Gardens, Kew, U.K. 

Description

Erect or decumbent annual or perennial herbs or subshrubs, very rarely woody, sometimes reduced to a single pair of leaves. Epidermis smooth or covered in papillae with the appearance of crystals (Mesembryanthemum crystallinum L. - ice-plant). Leaves almost always opposite, succulent, often cylindric and sometimes truncate (Lithops N.E.Br., Conophytum N.E.Br.), rarely with a spiny appendix at the apex (Trichodiadema Schwantes), margins entire or sometimes toothed. Flowers hermaphrodite, mostly solitary or in small cymes, pedicellate to sessile; calyx 3-5(-8) parted, cup-shaped, green; corolla absent and replaced by (4-)5-many staminodes, sometimes very colourful and showy, often resembling Compositae; stamens 5-numerous; stigmas free, sometimes united at base, ovary superior, semi-inferior or inferior, (2-)5-many locular, locules 1-many-seeded. Fruit a indehiscent berry or more often a loculicidal capsule; seeds small to medium, cochleariform, testa cells smooth, often brown or black.

Notes on delimitation

  • The Aizoaceae is one of the succulent families placed within the Caryophyllideae, order Caryophyllales (Behnke & Mabry, 1994), presenting betalain as the main pigment of flowers and stems and specialized photosynthesis often found in xerophytes, such as CAM and C3.
  • This family has been previously subdivided into Aizoaceae, Mesembryanthemaceae and Molluginaceae (Jacobsen, 1970).
  • The present circumscription follows Bittrich & Hartmann (1988), Hartmann (1990), Behnke & Mabry (1994) and Eggli (1994) and excludes the Molluginaceae.

Distribution in the Neotropics

  • An important family in South Africa (over 2,000 species), it is represented only by a few species that occur in disturbed environments, especially in the arid regions and by the seaside.

Distinguishing characters (always present)

  • Succulence of leaves.
  • 'Corolla' of staminodial origin.

Other important characters

  • Leaves opposite (often).
  • Flowers open at noon.
  • Capsular fruits that open when wetted.

Key differences from similar families

  • Unlike Cactaceae, where succulence is found on stems and leaves (which are alternate if present) in the Aizoaceae the succulence is confined to their (generally opposite) leaves.
  • Aizoaceae differs from Portulacaceae in opposite leaves and many strap-like perianth segments of staminodial origin.
  • It can be separated from the Molluginaceae because of its succulence and generally colourful and showy flowers, while Molluginaceae are not succulent and have white, small flowers.

Number of genera

  • Aptenia cordifolia (L.f.) Schwantes - originally from South Africa, widely cultivated as an ornamental and escaped in arid regions; creeping plants with relatively small (c. 1.5 cm long) pink flowers. 
  • Lampranthus N.E.Br. - genus with over 180 South African species, a few cultivated as ornamental in the Neotropics; perennial subshrub with showy, daisy-like flowers.
  • Mesembryanthemum crystallinum - originated in Africa and widely cultivated throughout the world; annual herbs sometimes covered with epidermic papillae resembling crystals.
  • Sesuvium portulacastrum L. - pantropical weed from coast and salt-lakes; halophytic herb with reddish stems; erect succulent herb with small, white flowers and drupaceous, spiny fruits, leaves deltoid.
  • Tetragonia tetragonioides (Pall.) Kuntze - grown as spinach throughout the Neotropics, sometimes naturalized.

Useful tips for generic identification

  • Ovary placentation.
  • Fruit structure and dehiscence.
  • Number of staminodes.
  • Number of calyx -lobes.
  • Leaf-shape and size.
  • Habit.

Notable genera and distinguishing features

See above

Status

  • The Aizoaceae are extremely rich in Africa, especially in South Africa. Mostly widespread genera that are introduced and naturalized in the Neotropics.

General notes

  • Of the several ornamental genera grown, the most notable are the succulents Lithops and Conophytum, the stone plants, which consist of a pair of truncate leaves, often with translucent 'windows' to allow sunlight in.
  • Amongst the members of Aizoaceae with showy flowers, the anthesis is determined by the presence of sunlight, with flowers opening at noon and closing after a few hours to re-open the next day, lasting a few days.
  • The staminode-formed 'corolla' has a unique anthesis method as it grows while the flower opens, with the inside of the staminodes expanding to cause the flower to open and the outside of the staminodes growing as the flower closes at the end of the period.
  • The capsular fruits of some genera open by means of special structures when wetted and close when dry, releasing the seeds gradually.

Important literature

Behnke, H.D. & Mabry, T.J. 1994 (eds.) Caryophyllales Evolution and Systematics. Springer-Verlag, Berlin, 334 p.

Bittrich, V. & Hartmann, H.E.K. 1988. The Aizoaceae - a new approach. Bot. Journ. Linn. Soc. 97: 239-254.

Eggli, U. 1994. Sukkulenten. Ulmer, Stuttgart, 336 p.

Hartmann, H.E.K. 1990. Aizoaceae in Kubitzki, K. (ed.) The Families and Genera of Vascular Plants II. Springer-Verlag, Berlin, pp. 37-69.

Jacobsen, H. 1970. Lexicon of Succulent Plants, 2nd ed. Blandford Press, Poole, Dorset, 682 p.

How to cite

Taylor, N. & Zappi, D. (2009). Neotropical Aizoaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Aizoaceae.htm.