Neotropical Mayacaceae

Description

Aquatic, perennial, rooted herbs. Leaves simple, spirally arranged, flat, sessile, without a distinct sheath, lanceolate to linear or nearly filiform, apically bidentate. Flowers axillary, solitary on short pedicels, emergent, actinomorphic, perfect, hypogynous, trimerous, with distinct calyx and corolla; sepals 3, free, opposite, green, valvate to subvalvate; petals 3, free, white, imbricate, short-clawed; stamens 3, alternate with petals; filaments slender, glabrous; anthers basifixed, tetrasporangiate to bisporangiate, opening by apical pores or pore-like slits or sometimes by pores at end of a tubular apical appendage; ovary unilocular, composed of 3 united carpels, placentation parietal; style simple, terminal; stigma short capitate or slightly trifid; 6-30 ovules/carpel, bitegmic, tenuinucellate. Fruit a loculicidal capsule with 3 lines of dehiscence, each midway between a placenta; seeds ovoid to globose, striate.

Notes on delimitation

• Mayacaceae belongs within the Order Poales, but differ vegetatively from most of the other members of this order.
• Anthers in some species are monothecal, the nucellar epidermis is basally thickened and the outer layer of the endosperm has proteins.
• The inflorescence is sometimes described as being terminal, but the flowers of the Neotropical species studied seem to be axillary and associated with a broad, adaxial prophyll-like structure.
• However, given the association of Mayacaceae with families that have scapose inflorescences with involucral bracts, the inflorescence of Mayacaceae deserves re-examination.

Distribution in the Neotropics

• Mayaca Aubl. (ca. 10 spp., Central America to Paraguay).

Distinguishing characters (always present)

• Mayacaceae are small herbs of marshes looking rather like club-mosses.
• They have numerous spirally-arranged, apically-toothed leaves, borne scattered along the stem.
• Pink to white apparently axillary flowers.
• Clearly differentiated calyx and corolla.

(Stevens 2009)

Other important characters

• Roots, stems and leaves contain vessels with scalariform perforations (Stevenson 1998).

Key differences from similar families

Differs from other aquatic plants such as:

• Pontederiaceae, which have inflated petioles and flowers arranged in dense inflorescences.
• Haemodoraceae, where the calyx and corolla are fused and septal nectaries present.

Number of genera

One Neotropical genus: Mayaca.

Useful tips for generic identification

• See family description.

Notable genera and distinguishing features

• Mayaca: anthers with slit or apical, poricidal dehiscence.

Status

• Most species are native to Tropical and warm-temperate America.
• One species occurs in tropical West Africa.

Important literature

Stevenson, D.W. 1998. Mayacaceae. In K. Kubitzki (ed.) The families and genera of vascular plants - Volume 4. Springer Verlag. Berlin, p. 294-296.

Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, February 2009 [and more or less continuously updated since]. http://www.mobot.org/MOBOT/research/APweb/.