Kingdom: Plantae
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Asparagaceae
Subfamily: Agavoideae
Genus: Agave
Species: A. attenuata
Binomial name: Agave attenuata
Synonyms: Agave cernua, Agave glaucescens, Agave pruinosa, Agave kellocki, Agave attenuata var. compacta, Agave attenuata var. latifolia, Agave attenuata var. paucibracteata, Agave attenuata var. subdentata, Agave attenuata var. subundulata,
Common names: Swans Neck Agave, Fox Tail Agave, Lion's Tail, Swans Neck, Elephant’s trunk, Spineless Century Plant, Gooseneck Succulent, Soft Leaved Agave, Soft Leaved Agave, Lions Tail Agave, Foxtail Agave.

Agave attenuata is a native to the plateau of the State of Jalisco in central Mexico. This agave is now rare in the wild.
Agave attenuata forms rosettes (>1.2m) of succulent-like, soft fleshy, lime green to bluish, 60cm, leaves. The leaves have no teeth on their margins, nor any terminal spines.
Some of its common names relate to the plant's development of an unusually curved raceme(inflorescence). This dense arching raceme can grow up to 7 m in length and has creamy coloured flowers. It may take up to 10 years for the Agave attenuata to bloom (although this varies with the location of the plant). After flowering the plant dies and suckers from the new plant will form at the bottom of the old plant.

Agave attenuata Swans Neck Agave.JPG The flowers on the lower section of the raceme.
Agave attenuata Swans Neck Agave-001.JPG

A section of the spike above the flowers.
Agave attenuata Swans Neck Agave-003.JPG

The end of the spike.
Agave attenuata Swans Neck Agave-002.JPG 

Thanks to Wikipedia for text and information: