Up to 1934, Agave, the "Century Plant', was classified in the Amaryllis Family and Yucca, the 'Adam's Needle', in the Liliaceae. In that year John Hutchinson of Kew realized that there was a strong affinity between the two genera (14.1) and placed them together in a new Family by themselves, the Agavaceae. His decision has been amply supported by later work, notably on the chromosomes and embryology. Yucca includes a number of hardy species and has fibrous, non-succulent leaves: it will not be considered further here.
No tabulation of the genera of the Agavaceae is given here because the limits of the Family are still being worked out, and a full discussion of the different viewpoints would be out of place. It will suffice to mention by name a few obviously related plants, mostly from the New World semi-deserts, that border on being succulents and certainly consort well with them in mixed plantings.
Agave has more or less succulent leaves, but they are also rich in fibre, making it one of the few succulents of economic value—the source of sisal hemp. Agaves are plants of such striking appearance that they are hardly likely to be mistaken for anything but a few of their close allies. The leaves are always arranged in a basal, stemless rosette, which may remain solitary or form clusters by suckering. The size ranges from A. pumila (14.2), at home in an 8cm (3in) pot, up to the largest of all leaves in succulents, 2m (6Hft) or more long, 0.5m (20in) thick at the base and proportionately wide. The leaves are long and tapered, stiff and outstretched, with a needle-like tip that may be several centimetres long, and sometimes fearsome curved prickles along the margins (2.16, 14.4). Truly they are plants to command respect, and. as with opuntias, one handles them with care. The larger species make an excellent impenetrable boundary fence. An attraction of many is the back of the leaf, which bears the imprint of adjacent leaves from the bud.
A legend dispelled. Agave is responsible for the original legend that cacti flower once in 100 years. Not only is agave totally unrelated to the Cactaceae. but the interval from germination to blooming is on average much less than a century. Some have been recorded as living for 70 years before blooming, but others perform in seven years. Flowering terminates the life of the plant, which pours all its accumulated energies into a spectacular display: a central panicle that grows 15-30cm (6-12in) a day, and becomes covered with many thousands of blooms. The flowers have six similar perianth members and secrete copious nectar, which attracts hummingbirds. The fruit is a stout three-chambered capsule packed with flat black seeds (2.20). As the fruits ripen, the leaf rosette withers and dies, but some species throw up suckers that grow into new plants. Others produce adventitious buds on the inflorescence that drop off and similarly
Below (14.2): Smallest olall agaves. Agave pumila is at home in an 8cm (3%in) pot.
prize for the most bizarre corkscrew leaf tips of all. A rather distinct subgenus, sometimes recognized as a separate genus Manfreda. has softer, only slightly fleshy leaves, usually dappled with brownish pink. A. maculosa is an example that will flower within a few years in a 12cm (5in) pot.
Agaves thrive in a rich soil, if it is porous, and need plenty of water in summer. If kept dry in winter they need no more heat than suffices to keep out the frost —indeed, many need no heat at all (6.12). In humid climates such as that of northern Europe the greatest danger outdoors is water collecting in the centre of the crown, which causes rot (6.14). It can be prevented by a glass or plastic canopy overhead, or by planting the rosette more-or-less vertically on rock-
Right(l4 3): Agave stricta in a Barcelona park Agaves are lough, trouble-tree and need little attention, but must be carefully sited because of their fierce armature
Below left( 14.4): Agave shawii in the Arroyo Seca Baja California After flowering, the rosette will die II rarely offsets, and propagates itself almost entirely by seed.
Below (14.5): Agave victoria-feginae. one of the slowest growing of succulents It is among the most highly prized agaves lor exhibition give rise to daughter plants.
Agave is an exclusively New World genus, being centred in Mexico and extending into the southern USA. the West Indies and northern South America. A. americana was introduced to Europe in 1561, or perhaps even earlier, and created a sensation when it first flowered in 1586. Thereafter we have a series of reports of this event, which never fails to arouse wonder even today: in the largest growing species the axis may exceed 11 m (37ft) in height. An early rumour arose that the emergence of the flower stem was accompanied by a great explosion, apparently because of a mistranslation of a French writer who said that flowering caused "un grand eclat"! More recently an enterprising practical joker took serial photographs of a flower stem over a period of weeks and hoaxed a newspaper into publishing them with a sensational story that it all happened in a matter of minutes! A flowering agave may be a source of embarrassment in a small glasshouse. If it happens in the summer, the usual procedure is to remove glass from the roof and allow the inflorescence to soar skywards.
Some larger agaves have become semi-naturalized following their introduction to countries bordering the Mediterranean.
and contribute much to the exotic look of holiday resorts. Especially fine are the variegated cultivars. In A. americana alone there are at least seven different striped variants, surely not only the finest in succulents but among the most spectacular of all variegated plants.
Agaves in cultivation. In countries where succulents must be grown under glass, agaves would surely be more popular if they took up less space. Although their tough foliage allows them to stand outdoors during the summer, they must be carefully positioned in winter to avoid contact with passers-by (14.3). and a specimen that has to have its leaf tips trimmed off is worse than no specimen at all. There are, however, many smaller, solitary species, of which the best known is A. victoria-reginae (14.5), with hemispherical rosettes of 12-15cm (5-6in) stiff, blackish green leaves with black spiny tips and attractive white longitudinal markings. It is exceedingly slow growing, and large specimens are always treasured showpieces. In a related group the species have the leaf margins split off intocurling white fibres. A. schidigera is the finest of these, and A. pa rviflora a perfect miniature. A. utahensis in some of its forms wins the
work. The tough leavesare resistant toall common pests except the worst of all. Homo sapiens, who feels impelled to carve his initials and leave a scar on the leaf for life. Suitable chemical deterrents exist, but the law prevents their use!
Other important genera. Dracaena draco is the 'Dragon Tree' of the Canary Islands, capable of reaching an enormous height and bulk in old age. Nolina recurvata and Calibanus hookeri produce a massive more-or-less spherical caudex from which arise fountain-like rosettes of long, narrow, fibrous recurving leaves.
Finally, from Africa there is the large genus Sansevieria. whose species typically spread by means of massive underground stems. The few leaves are cylindrical, channelled or flat, very tough and long-lived, and so fibrous that they provide the bowstring hemp of commerce—a parallel development to agave. Sansevieria provides us with some of the most adaptable and long-suffering of all house plants, ideally suited to windowsills in centrally heated rooms where little else will survive. The species with blotched or variegated leaves are the most favoured, notably cultivars of 5. trifas-ciata. In addition to standing full sun, they can survive in deep shade, although they then grow very slowly and must be watered cautiously or they rot off. About the only thing that deters Sansevieria is frost: a winter minimum of 10°C (50°F) should be the aim.
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