Agavaceae
Plants usually perennial, occasionally epiphytic, sometimes monocarpic or polycarpic, monoecious, dioecious, or polygamodioecious, small to gigantic, sometimes arborescent, usually scapose. Stems subterranean or aboveground, sometimes branched. Leaves simple, annual or long-lived, in terminal rosettes or occasionally cauline, sessile or occasionally pseudo-petiolate; blade linear, lanceolate, oblanceolate, ovate, or elliptic, fibrous, thin and flexible, thick and rigid or succulent, or fibrous, often glaucous, margins entire, serrulate, dentate, denticulate, corneous, or filiferous, apex rigid or flexible, sometimes pungent, often with short or long spine. Inflorescences terminal or axillary spikes, racemose or paniculate, sometimes umbellate, bracteate, often huge; bracts ascending or erect, occasionally reflexed, leaflike proximally, scalelike distally. Flowers 6-merous, bisexual or functionally unisexual; perianth of 2 similar petallike whorls, semisucculent; tepals distinct or connate into tube, apex glandular or glandular-pubescent; stamens included or exserted; filaments often broadened and succulent, glabrous, pubescent, or papillose; anthers versatile, dehiscence longitudinal; ovary superior or inferior, 3-locular or occasionally 1-locular, 3-angled, ovoid, or cylindrical, with axillary or rarely parietal placentation; style included or exserted; stigmas 1 or 3, 3-lobed or capitate; pedicel usually distinct, articulate or not, rarely absent. Fruits occasionally baccate, usually capsular and sometimes winged or lobed, or indehiscent and dry or fleshy. Seeds 1–3(–many) per locule, flattened, 3-angled, hemispheric, ovoid, obovoid, or globose.
Distribution
Worldwide, primarily arid, semitropical, subtropical, and tropical regions.
Discussion
Genera 17 or 18, species ca. 550 (9 genera, 84 species in the flora; 2 genera, 6 species introduced).
There is little agreement on the treatment of Agavaceae. The group containing Agave, Yucca, Furcraea, Hesperaloe, and Manfreda generally has been accepted as the core of Agavaceae, or as subfamilies Agavoideae and Yuccoideae, but treatment of Dracaena, Sansevieria, Cordyline, Nolina, and Dasylirion has been varied. A. L. Takhtajan (1987) and R. F. Thorne (1992b) placed these genera in Dracaenaceae but treated them at different levels. Takhtajan located them in the subfamily Dracaenoideae within sections Nolineae (Nolina and Dasylirion), Sansevierieae (Sansevieria), and Dracaeneae (Cordyline and Dracaena). Thorne, on the other hand, placed these same groupings at the subfamily level. R. M. T. Dahlgren et al. (1985) recognized them as separate families, Nolinaceae (Nolina and Dasylirion), Dracaenaceae (Sansevieria and Dracaena), and Asteliaceae (Cordyline), in addition to the Agavaceae (Yucca, Hesperaloe, Agave, Manfreda, and Furcraea).
A. Cronquist (1981) based his broadly circumscribed Agavaceae on a common xerophytic habit. However, the karyotype of 5 long and 25 short chromosomes for the Agavoideae and Yuccoideae is distinct from the karyotypes of the other subfamilies that Cronquist included in the Agavaceae. Current research on the phylogenetics of moncotyledons, using DNA sequences of rbcL, support the separation of Dracaena, Nolina, and Dasylirion from Agavaceae (M. R. Duvall et al. 1993b). We believe that a broad interpretation of the Agavaceae unites groups that should be recognized as separate.
Many genera in Agavaceae are economically important. All genera in the Agavoideae and Yuccoideae contain steroidal sapogenins; some have been used in folk medicine, and locally and commercially as soap (G. Blunden et al. 1978; S. E. Verhoek 1978; M. Wall et al. 1957). They provide fibers for cordage, baskets, and hats, as well as food and drink for many indigenous peoples of the southwestern United States (H. S. Gentry 1982). They are also used as commercial fiber and beverage crops in Latin America and the Old World (H. Brucher 1989). In the southern United States, some species in each genus are cultivated and represented in the flora, and at least one species of Yucca is now grown as far north as Canada. Collectors should record the uses of these plants in their notes along with the critical information on plant habit and morphology. Photographs are often important tools for the identification of these plants, and, with the advent of digital cameras, are now much easier to obtain and process.
Selected References
Lower Taxa
Illustrations
Key
| 1 | Ovary inferior. | > 2 |
| 1 | Ovary superior. | > 4 |
| 2 | Stems subterranean; leaf apex flexible. | Manfreda |
| 2 | Stems aboveground; leaf apex rigid. | > 3 |
| 3 | Leaf apex abruptly narrowed, with long spine; flowers erect or recurved; style subulate, filaments filiform. | Agave |
| 3 | Leaf apex blunt; flowers drooping; style and filaments abruptly swollen in proximal half. | Furcraea |
| 4 | Flowers functionally unisexual; fruits capsular; tepals no longer than 5 mm. | > 5 |
| 4 | Flowers bisexual; fruits capsular or baccate; tepals longer than 5 mm. | > 6 |
| 5 | Capsules 3-locular, dehiscent; seeds globose; leaf blade not fibrous, margins entire or serrulate. | Nolina |
| 5 | Capsules 1-locular, indehiscent; seeds 3-angled; leaf blade fibrous, margins with sharp, curved prickles. | Dasylirion |
| 6 | Fruits baccate; seeds 1–3. | Sansevieria |
| 6 | Fruits capsular, rarely baccate; seeds many. | > 7 |
| 7 | Perianth narrowly tubular to broadly campanulate; filaments glabrous; capsules ovoid. | Hesperaloe |
| 7 | Perianth campanulate or globose; filaments smooth or papillose; capsules almost never ovoid. | > 8 |
| 8 | Fruits erect or pendent, usually indehiscent, occasionally dehiscent and septicidal; scape usually less than 2.5 cm diam.; bracts usually ascending. | Yucca |
| 8 | Fruits erect, dehiscent and loculidical; scape usually more than 2.5 cm diam.; bracts usually reflexed. | Hesperoyucca |