Agavaceae Endl.
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; edgewise to the stem, or with ‘normal’ orientation; 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). Leaves with a persistent basal meristem, and basipetal development. |
General anatomy. Plants without silica bodies. Accumulated starch other than exclusively ‘pteridophyte type’.
Leaf anatomy. Stomata present; anomocytic.
The mesophyll not containing mucilage cells; containing calcium oxalate crystals. The mesophyll crystals raphides and solitary-prismatic. Vessels absent.
Stem anatomy. Nodes multilacunar. Primary vascular tissue in scattered bundles. Secondary thickening absent, or anomalous (e.g. Agave, Furcraea, Yucca); when present, from a single cambial ring. 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 unit 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, biochemistry. Not cyanogenic. Alkaloids absent (?). Proanthocyanidins absent. Flavonols present (Agave), or absent; in Agave, kaempferol. Ellagic acid absent. Saponins/sapogenins present (richly, steroidal, including those of Agave and Yucca which constitute active principles of contraceptive pills). CAM. CAM recorded directly in Agave, Hesperaloë, Polianthes, Yucca (non-succulent).
Geography, cytology. Holarctic and Neotropical. Madrean. Sub-tropical to tropical. Widespread. X = 30 (consistently).
Taxonomy. Subclass Monocotyledonae. Superorder Liliiflorae; Asparagales. APG (1998) Monocot; non-commelinoid. APG 3 (2009) Order: Asparagales.
Species about 400. Genera 9; Agave, Beschorneria, Furcraea, Hesperaloë, Littaea, Manfreda, Polianthes, Prochnyanthes, Yucca.
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..
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