Neotropical Alzateaceae

Sue Frisby

Royal Botanic Gardens, Kew, UK. 

Description

Variable habit: from trees up to 20m to slender high-climbing hemiepiphytes with a tendency to a multi-trunked growth form, stilt roots and sometimes developing a strangler habit. Stems: branches opposite or whorled, with very strongly tetragonal thickish twigs; young stems winged, mature branches round in cross-section; jointed stems with strong interpetiolar ridges and swollen nodes, purple-red before peeling to become red-brown with age. Stipules intrapetiolar, 2 or more at the base of the petiole. Stem wings on flowering branches also extended at the nodes into stipule -like projections. Leaves mostly clustered at the apices of branches, opposite or whorled, simple, entire, very coriaceous, oblong-obovate, elliptical or oblong-ovate, glabrous, lustrous above, shortly petiolate to sessile, pinnately veined (brochidodromous) with faint secondary veins not differentiated from the parallel inter-secondary veins. Inflorescence a terminal thyrse (paniculate cyme) 10-30 flowered, ebracteolate. Flowers small, campanulate actinomorphic, bisexual, apetalous, a single perianth whorl of 5 thick fleshy, partly united, valvate lobes, coriaceous, persistent, yellowish green, conical in bud; short hypanthium present, nectary disc lobed, extending from the ovary to the sinuses of the calyx lobes; androecium of 5 equal, fertile stamens, alternating with the calyx lobes, free of the perianth (on the hypanthium), filaments green, stout, short (as long as the anthers) dorsifixed, introse, the connective broadly expanded, heart-shaped, pink with white edges, fleshy, at anthesis held at right angles to the filament with the distal apiculate apex extending out of the calyx between the perianth lobes, thus simulating petals, anthers dehiscing via longitudinal slits; gynoecium syncarpous, slightly bilaterally flattened, superior, bicarpellate, bilocular ovary, placentation parietal, with shortly style and capitate stigma. Fruit a small, round, fleshy, dry, indurate, dehiscent, loculicidal capsule. Bilaterally compressed, horizontally flattened, striated, subtended by persistent calyx, yellow - becoming reddish in ripening; seeds numerous, flattened, oblong, fragile, surrounded by small membranous wing, suggesting wind dispersal.

Notes on delimitation

  • Relationships suggested by various authors since 1794 encompass eight families in five orders.
  • Systematic placement has included: Santalaceae, Celastraceae, Lythraceae, Crypteroniaceae, Rhamnaceae, Melastomataceae and Flacourtiaceae.
  • Alzateaceae is most probably a member of the order Myrtales with characters such as internal phloem, vestured pits, flavonols in the leaves and ellagic acid.
  • Major differences from all other families of Myrtales in morphology and embryology are sufficient for Alzateaceae to stand as a separate monotypic family.
  • DNA studies recently confirm that Rhynchocalycaceae is the most closely related family and also monotypic.

Distribution in the Neotropics

  • This monotypic family is represented by Alzatea verticillata Ruiz & Pav. which occurs in wet montane cloud forests at elevations from 900 to 2,200 ( - 3,000) meters in Costa Rica, Ecuador, Panama, Peru, Bolivia, and Colombia. It is distributed along the lower slopes of the Andes in Peru and Bolivia, in humid forests of the Upper Amazon basin and also in the cloud forests of  Costa Rica and Panama.
  • Alzatea verticillata subspecies amplifolia S.A. Graham has larger more oval, sessile or subsessile leaves and is distributed through Costa Rica and Panama.
  • Alzatea verticillata subspecies verticillata Ruiz & Pav. has smaller leaves with petioles and is distributed through the eastern escarpment of the Andean Mountains in South America.

Distinguishing characters (always present)

  • Habit: Variable habit from small trees to slender high-climbing hemi-epiphytes with a tendency to a multi-trunked growth form, stilt roots and sometimes developing a strangler habit.
  • Stems: strongly tetragonal, thickish young branches, jointed with swollen nodes and strong interpetiolar ridges.
  • Leaves: Clusia-like, thick and coriaceous, oval with rounded apex and base with very short petiole. Secondary veins immersed or slightly prominulous below.
  • Inflorescence: small with superior ovary, hypanthium present, corolla absent.
  • Fruit: dry loculicidal capsules, slightly laterally compressed, subtended by persistent calyx.
  • Seeds: 40-60 winged, membranaceous and fragile.
  • Anatomy: vestured pitting of the vessel elements, internal phloem, ellagic acid produced in the leaves, branched sclereids occur in the leaf palisade tissue, stems with trilacunar, three trace nodes and bisporic Allium type embryo sac.

Key differences from similar families

The families below differ from Alzateaceae in the following characters:

  • Santalaceae:  No ellagic acid produced or internal phloem.
  • Celastraceae: Sepals and petals are mostly imbricate, has axile placentation, no internal phloem with seeds which are often arillate with abundant endosperm.
  • Rhamnaceae: No internal phloem, ellagic acid, vestured pitting of vessel elements nor wings on seeds plus it has drupaceous fruits (not dry capsules).
  • Flacourtiaceae: Leaves usually alternate.

Myrtales:

 

Number of genera

  • 1: Alzatea Ruiz & Pav. (one species)
  • The two subspecies which are recognised (amplifolia in the north and verticillata in the south) are only minimally distinct and some partially intermediate representatives do occur near the border of Ecuador and Peru.

Status

  • Native to Neotropics.

Important literature

Graham, S.A. 1984. Alzateaceae, A New Family Of Myrtales In The American Tropics. Annals Of The Missouri Botanical Garden. 71:757-779.

Pennington, T.D., Reynel, C., Daza, A. 2004. Illustrated Guide To The Trees Of Peru. David Hunt Press, Sherborne 551.

Schonenberger, J., Conti, E. 2003. Molecular Phylogeny And Floral Evolution Of The Penaeaceae, Oliniaceae, Rhynchocalycaceae, And Alzateaceae (Myrtales). American Journal of Botany 90 (2): 293-309.

Silverston-Sopkin, P.A., Graham, S.A. 1986. Alzateaceae, A Plant Family New To Colombia. Brittonia 38 (4) : 340-343.

How to cite

Frisby, S. (2009). Neotropical Alzateaceae. 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/Alzateaceae.htm.