The families of flowering plants


L. Watson and M. J. Dallwitz

Agavaceae Endl.

~ Former Liliaceae, Asparagaceae-Agavoideae p.p.

Including Yuccaceae J.G. Agardh; excluding Doryanthaceae, Dracaenaceae, Phormiaceae.

Habit and leaf form. Herbs, or shrubs, or ‘arborescent’ (often ‘rosette trees’). ‘Normal’ plants. Leaves well developed. Plants succulent, or non-succulent. Perennial; with a basal aggregation of leaves, or with terminal aggregations of leaves (when shrubby or arborescent); rhizomatous. Self supporting, or epiphytic. Often pachycaul. Xerophytic. Leaves evergreen; small to very large; alternate; spiral; flat, or terete; leathery, or fleshy, or leathery and fleshy; sessile; sheathing; borne edgewise to the stem, or ‘normally orientated’; simple; epulvinate. Lamina entire; linear, or lanceolate, or subulate; parallel-veined; without cross-venules. Lamina margins entire, or serrate (often sharp pointed and with lateral spines). Leaf development ‘graminaceous’.

General anatomy. Plants without silica bodies.

Leaf anatomy. Stomata present; anomocytic. The mesophyll not containing mucilage cells; containing calcium oxalate crystals. The mesophyll crystals raphides and solitary-prismatic. Foliar vessels absent.

Axial (stem, wood) anatomy. Nodes multilacunar. Primary vascular tissue consisting of scattered bundles. Secondary thickening absent, or anomalous (e.g. Agave, Furcraea, Yucca). The anomalous secondary thickening when present, from a single cambial ring. The axial xylem without vessels.

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

Reproductive type, pollination. Plants hermaphrodite (usually), or andromonoecious, or gynomonoecious, or dioecious. Floral nectaries present. Nectar secretion from the gynoecium (from septal nectaries).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in panicles. The ultimate inflorescence units cymose (but often condensed). Inflorescences scapiflorous, or not scapiflorous; terminal; usually large, much-branched panicles; espatheate. Flowers bracteate; regular to somewhat irregular; when irregular, somewhat zygomorphic; 3 merous; cyclic; pentacyclic. Perigone tube present, or absent.

Perianth of ‘tepals’; 6; free, or joined (below); 2 whorled; isomerous; petaloid; similar in the two whorls.

Androecium 6. Androecial members adnate (to the perianth tube), or free of the perianth; all equal; free of one another; 2 whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 3. Stamens 3, or 6; isomerous with the perianth, or diplostemonous. Anthers dehiscing via longitudinal slits; usually introrse; tetrasporangiate; unappendaged. Endothecium developing fibrous thickenings. Microsporogenesis successive. The initial microspore tetrads tetrahedral, or isobilateral, or linear. Anther wall of the ‘monocot’ type. Tapetum glandular. Pollen shed in aggregates (rarely), or shed as single grains; in Agave, occasionally in tetrads. Pollen grains aperturate; 1 aperturate, or 2 aperturate; sulcate, or sulculate; 2-celled.

Gynoecium 3 carpelled. The pistil 3 celled. Gynoecium syncarpous; eu-syncarpous; superior to inferior. Ovary 3 locular. Gynoecium stylate. Styles 1; apical. Stigmas wet type, or dry type; papillate; Group II type, or Group III type, or Group IV type. Placentation axile. Ovules 6–50 per locule (i.e. ‘several to many’); anatropous; crassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating. Synergids pear-shaped (sometimes with filiform apparatus). Endosperm formation helobial, or nuclear (rarely).

Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule, or a berry. Capsules loculicidal. Seeds endospermic. Endosperm oily. Seeds without starch. Cotyledons 1. Embryo achlorophyllous (2/2 — Agave, Yucca); straight. Testa encrusted with phytomelan; black (where recorded).

Seedling. Hypocotyl internode present (short). Seedling collar not conspicuous. Cotyledon hyperphyll somewhat to much elongated; assimilatory; more or less circular in t.s. Coleoptile absent. Seedling cataphylls absent. First leaf dorsiventral. Primary root persistent.

Physiology, phytochemistry. CAM. CAM recorded directly in Agave, Hesperaloë, Polianthes, Yucca (non-succulent). Acumulated starch other than exclusively ‘pteridophyte type’. Not cyanogenic. Alkaloids absent (?). Saponins/sapogenins present (richly, steroidal, including those of Agave and Yucca which constitute active principles of contraceptive pills). Proanthocyanidins absent. Flavonols present (Agave), or absent; in Agave, kaempferol. Ellagic acid absent.

Geography, cytology. Holarctic and Neotropical. Madrean. Sub-tropical to tropical. Widespread. X = 30 (consistently).

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Liliiflorae; Asparagales. APG 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; Order Asparagales (as a synonym of Asparagaceae).

Species about 400. Genera 9; Agave, Beschorneria, Furcraea, Hesperaloë, Littaea, Manfreda, Polianthes, Prochnyanthes, Yucca.

General remarks. Conspicuously differing from Asparagaceae sensu stricto (q.v.) in habit and associated characters; also in assorted ‘esoteric characters’ which, in view of limited sampling, are of questionable taxonomic worth (e.g., xylem without vessels, the CAM physiology, seedlings without cataphylls.).

Economic uses, etc. Pulque and mescal derive from fermentation/distillation of Agave sap; and many Agave and Yucca species yield useful fibres (sisal hemp, henequen, pita, istle, ixtle, lechuguilla, keratto, etc.).

Illustrations. • Agave (technical details). • Habit. • Agave scabra: Bot. Reg. 1839, 55. • Yucca aloifolia: as Y. draconis, Bot. Reg. 1894 (1836). • Yucca cf. flaccida, filamentosa: as Y. flaccida, Bot. Reg. 1895 (1836). • cf. Yucca gloriosa: as Yucca superba, Bot. Reg. 1690, 1835. • Yucca spp..

This description is offered for casual browsing only. We strongly advise against extracting comparative information from it. This is much more easily achieved using 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).

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 2013.’.