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The families of flowering plants

L. Watson and M. J. Dallwitz

Acoraceae J.G. Agardh

~ Araceae — but seemingly very distinct.

Habit and leaf form. Paludal, aromatic herbs; bearing essential oils. Leaves well developed. Perennial; with a basal aggregation of leaves; sympodially rhizomatous. Helophytic. Leaves alternate; distichous; flat; sessile; sheathing; aromatic (tangerine- or cinnamon-scented); borne edgewise to the stem (ensiform); simple. Lamina entire; parallel-veined. Lamina margins entire; flat. Leaf development ‘graminaceous’ (?).

General anatomy. Plants without silica bodies.

Leaf anatomy. The leaf lamina bifacial. The mesophyll with spherical etherial oil cells; without crystals (and no raphides).

Axial (stem, wood) anatomy. Secondary thickening absent.

Root anatomy. Root xylem with vessels; vessel end-walls scalariform.

Reproductive type, pollination. Plants hermaphrodite (the flowers protogynous).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in spikes. Inflorescences scapiflorous (the scape keeled, with double vascularization, taken to represent adnation of the peduncle with the sheath of the subtending leaf); solitary, lateral spadices, tapering acropetally to a blunt tip, covered with tightly packed flowers; espatheate (in that the leafy point which terminates the scape above the manifestly lateral spadix seems to represent the blade of a terminal leaf, rather than a true spathe). Flowers ebracteate; ebracteolate; minute, or small; regular; 3 merous; cyclic; pentacyclic. Perigone tube absent.

Perianth of ‘tepals’; 6; free (the members concave or hooded); 2 whorled; isomerous; similar in the two whorls (membranous).

Androecium 6. Androecial members free of the perianth; free of one another; 2 whorled. Androecium exclusively of fertile stamens. Stamens 6. Anthers basifixed; dehiscing via longitudinal slits; introrse. Endothecium developing fibrous thickenings. The endothecial thickenings stellate. Microsporogenesis successive. Tapetum glandular. Pollen grains aperturate; 1 aperturate; sulcate (to sub-ulcerate); 2-celled.

Gynoecium (2–)3(–4) carpelled. Carpels reduced in number relative to the perianth, or isomerous with the perianth (usually), or increased in number relative to the perianth. The pistil (2–)3(–4) celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary (2–)3(–4) locular. Gynoecium stylate (the stigma sessile). Placentation axile to apical. Ovules 2–4(–5) per locule; pendulous; orthotropous; bitegmic. Embryo-sac development Polygonum-type. Endosperm formation cellular.

Fruit fleshy, or non-fleshy (?); dehiscent, or indehiscent (?); a capsule, or a berry (?). Seeds endospermic. Perisperm present. Cotyledons 1. Embryo chlorophyllous. Testa without phytomelan; thick.

Seedling. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; more or less circular in t.s. Coleoptile absent. Seedling cataphylls absent. First leaf ensiform. Primary root ephemeral.

Physiology, phytochemistry. Proanthocyanidins present.

Geography, cytology. Holarctic and Paleotropical. Frigid zone, temperate, and sub-tropical. Celebes and New Guinea, Eastern Asia to Norway approaching the Arctic circle, central and western North America. 2n=24. Supposed basic chromosome number of family: 12. Ploidy levels recorded: 2 and 3.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Ariflorae (? — perhaps meriting a monogeneric superorder, Acoriflorae); Arales (?). APG 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; Order formerly Alismatales (subsequently Acorales).

Species 2–6. Genera 1; only genus, Acorus.

General remarks. Grayum (1987) justified removal of Acorus from Araceae, and subsequent molecular analyses (e.g. Davis 1995) portray it, alone or with Gymnostachys, as the sister group of all other Monocotyledons. No double fertilization, cf. Orchidaceae.

Economic uses, etc. Oleum calami is distilled from the rhizomes of A. calamus, for use in perfumery and medicine.

Illustrations. • Acorus calamus, flowering plant (photo). • Acorus calamus, inflorescence (photo). • Acorus calamus, habitat (photo). • Acorus calamus (B. Ent., 1838). • Acorus calamus: Eng. Bot. 1391 (1869). • Acorus calamus: Gynoecium and fruit details.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 19th October 2016.’.