Agave sp.

 

Agave (/əˈɡɑːvi/; also UK: /əˈɡeɪvi/; Anglo-Hispanic, also US: /əˈɡɑːveɪ/) is a genus of monocots native to the hot and arid regions of the Americas and the Caribbean, although some Agave species are also native to tropical areas of North America, such as Mexico. The genus is primarily known for its succulent and xerophytic species that typically form large rosettes of strong, fleshy leaves. Agave now includes species formerly placed in a number of other genera, such as Manfreda, ×Mangave, Polianthes and Prochnyanthes.

Many plants in this genus may be considered perennial, because they require several to many years to mature and flower. However, most Agave species are more accurately described as monocarpic rosettes or multiannuals, since each individual rosette flowers only once and then dies; a small number of Agave species are polycarpic. Maguey flowers are eaten in many indigenous culinary traditions of Mesoamerica.

Along with plants from the closely related genera Yucca, Hesperoyucca, and Hesperaloe, various Agave species are popular ornamental plants in hot, dry climates, as they require very little supplemental water to survive. Most Agave species grow very slowly. Some Agave species are known by the common name "century plant".

Description

The succulent leaves of most Agave species have sharp marginal teeth, an extremely sharp terminal spine, and are very fibrous inside. The stout stem is usually extremely short, which may make the plant appear as though it is stemless.

Agave rosettes are mostly monocarpic, though some species are polycarpic.  During flowering, a tall stem or "mast" ("quiote" in Mexico), which can grow to be 12 metres (40 feet) high, grows apically from the center of the rosette and bears a large number of short, tubular flowers and sometimes vegetatively produced bulbils (a form of asexual reproduction). After pollination/fertilization and subsequent fruit development, in monocarpic species, the original rosette dies. However, throughout the lifetime of many Agave species, rhizomatous suckers develop above the roots at the base of the rosette.  These suckers go on to form new plants after the original rosette desiccates and dies. Not all agaves produce suckers throughout their lifetimes; some species rarely or never produce suckers, while others may only develop suckers after final maturation with inflorescence. Some varieties can live for 60 years before flowering.

Agaves can be confused with cacti, aloes, or stonecrops, but although these plants all share similar morphological adaptations to arid environments (e.g. succulence), each group belongs to a different plant family and probably experienced convergent evolution. Further, cactus (Cactaceae) and stonecrop (Crassulaceae) lineages are eudicots, while aloes (Asphodelaceae) and agaves (Asparagaceae) are monocots.

Adaptations

The agave root system, consisting of a network of shallow rhizomes, allows the agave to efficiently capture moisture from rain, condensation, and dew. In addition to growing from seeds, most agaves produce 'pups' – young plants from runners. Agave vilmoriniana (the octopus agave) produces hundreds of pups on its bloom stalk. Agave leaves store the plant's water and are crucial to its continued existence. The coated leaf surface prevents evaporation. The leaves also have sharp, spiked edges. The spikes discourage predators from eating the plant or using it as a source of water and are so tough that ancient peoples used them for sewing needles. The sap is acidic. Some agaves bloom at a height up to 9 m (30 ft) so that they are far out of reach to animals that might attack them. Smaller species, such as Agave lechuguilla, have smaller bloom stalks.

Taxonomy

The genus name Agave come from the Ancient Greek αγαυή agauê from ἀγαυός agauós meaning "illustrious, noble" having to do with very tall flower spikes found on its many species.

The genus Agave was erected by Carl Linnaeus in 1753, initially with four species. The first listed was Agave americana, now the type species. In the Cronquist system and others, Agave was placed in the family Liliaceae, but phylogenetic analyses of DNA sequences later showed it did not belong there. In the APG II system, Agave was placed in the segregated family Agavaceae. When this system was superseded by the APG III system in 2009, the Agavaceae were subsumed into the expanded family Asparagaceae, and Agave was treated as one of 18 genera in the subfamily Agavoideae, a position retained in the APG IV system of 2016.

Agaves and close relatives have long presented significant taxonomic difficulty. These difficulties could be due to the relatively young evolutionary age of the group (major diversification events of the group most likely occurred 8–10 million years ago), ease of hybridization between species (and even genera), incomplete lineage sorting, and long generation times. Within a species, morphological variations can be considerable, especially in cultivation; a number of named species may actually just be variants of original wild-type species that horticulturalists bred to appear unique in cultivation.

Molecular phylogenetic analyses from 1996 onwards repeatedly showed that the previously separate genera Manfreda, Polianthes and Prochnyanthes were embedded in Agave, as traditionally circumscribed, making Agave paraphyletic.[18][13][19] These genera are now combined with Agave to form Agave sensu lato, which contains about 252 species total. Traditionally, the genus Agave was circumscribed to be composed of about 166 species.

In some of the older classifications, Agave was divided into two subgenera, Agave and Littaea, based on the form of the inflorescence. These two subgenera are probably not monophyletic. A 2019 classification uses three subgenera:

• Agave subg. Littaea (Tagl.) Baker (8 sections)
• Agave subg. Agave (22 sections)
• Agave subg. Manfreda (Salisbury) Baker (2 sections) – includes former genera Manfreda, Polianthes, Bravoa and Prochnyanthes

Hybrids between species in Agave subg. Manfreda and other species were given the nothogenus name ×Mangave when Manfreda was recognized as a separate genus.

Species

Main article: List of Agave species

Agave - Wikipedia

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