Plants of the genus Agave L. are currently increasing in popularity for use in landscaping, water-saving gardens and succulent collections. Although there has always been a core of common Agave species available in succulent collections, these have usually been species such as A. americana, A. attenuata, A. filifera, A. parvifora, A. polianthiflora and A. victoriae-reginae. At present there are undoubtedly more taxa of Agave available in Australia than ever before (Tables 1 and 2), and the recent publication of the gardener’s guide book on agaves and Yuccas by Mary and Gary Irish (2000) is testament to this popularity. Despite the great variety that is available, there are still some striking ornamental species such as A. impressa, A. marmorata and A. zebra that are apparently not in Australia.
The genus Agave is the largest of those included in the plant family Agavaceae, the others being Beschorneria, Furcraea, Hesperaloe, Hesperoyucca and Yucca. Species of Agave have been well known to humans for centuries, both for their use as a source of food, beverages (pulque, tequila), fibre (sisal hemp) and building materials in the New World, and as ornamentals in the western word. All species of Agave are endemic to the New World, ranging from the southern U.S.A., through Mexico (where the majority of species occur) into the Caribbean islands such as Cuba, Aruba, Hispaniola amongst others and into northern south America in the countries of Panama, Colombia and Venezuela. There is no comprehensive monograph for the genus with the excellent account of Gentry (1982) covering only continental North America (the U.S.A. and Mexico). A recent synopsis by Thiede (2001) in the ‘Illustrated Handbook of Succulent Plants – Monocotyledons’ covers some 210 species (including the subsumed genera Bravoa, Polianthes, Manfreda); however, it is not possible to identify plants with that account due to the lack of identification keys and comprehensive descriptions. Occasional new species are still being discovered in Mexico, but it is likely that the great descriptive phase of Agave systematics is now over.
Agave americana
var. americana 'Marginata'
Agave attenuata
All taxa of Agave are rosette succulents and flower terminally from the primary growing point, after which that particular rosette dies. In cases where the individual does not sucker, produce bulbils on the inflorescence, or requires a second individual to provide pollen to form viable seeds, then that particular clone dies. Conversely some species of Agave are profuse producers of suckers and/or bulbils, often resulting in adventive naturalisations in the Australian environment (e.g. A. americana, A. sisalana, A. vivipara). Individual rosettes may range from small miniatures no more than 10 cm across to massive giants nearly 4 m in diameter. Usually the leaves are armed with pungent terminal spines and marginal teeth and may be particularly vicious if accidentally encountered. A few species have soft teeth (e.g. A. gypsophila) or are totally unarmed (e.g. A. attenuata). Leaf colour is usually more or less concolorous (both sides of the leaf the same colour) and varies from
Agave filifera
uniformly glaucous-blue (e.g. A. americana, A. colorata, A. gypsophila)
to grey-green (e.g. A. sisalana, A.
vivipara), green (A. bovicornuta),
or even almost white (A. guiengola).
The leaves may have a banded pattern (A.
marmorata, A. zebra), imprinting of the leaf teeth on adjoining leaves
(A. americana, A. colorata),
white markings (A. victoriae-reginae,
A. parviflora) or marginal threads (A. filifera, A. parviflora, A. toumeyana) and vary in shape from
linear-terete, linear-lanceolate, lanceolate, ovate or obovate.
As with many succulent groups, there has been some selection of clones, particularly for those with variegated foliage. Probably A. americana has the greatest number of cultivars available (Tables 1, 2), and it is likely that more will appear in due course. Other notable cultivars are A. desmetiana ‘Golden Moments’, A. attenuata ‘Boutin Blue’ and ‘Emery Stripy’ and A. victoriae-
Agave horrida
with imprint of leaf teeth.
reginae ‘Golden Princess’. I have also seen variegated clones of A. lophantha and A. parryi var. patonii in cultivation in the U.S.A.
Agaves are usually easy to grow, especially in most of Queensland. Most species are tolerant of cold, but many would require protection where heavy frosts occur. The majority of species revel in bright light and hot conditions, particularly if planted out.
They are heavy feeders and can soon become pot-bound, indeed they have the remarkable ability to fill a pot with roots and to apparently completely absorb the potting mix. It is possible to trim the roots, thus extending the time that the individual is kept in a pot, although this is probably akin to a form of torture. If grown in pots (especially small ones), then it is essential that water is kept up to them during hot weather. They can also be literally cooked in a pot during heatwave conditions (e.g. A. victoriae-reginae) and can also be badly burnt if not conditioned to full sun or if the pot is moved around. Many of the smaller growing species (Table 1), especially the true miniatures such as A. parviflora or some forms of A. victoriae-reginae) will be happy for ever in a roomy pot and some species such as the unusual A. nizandensis will even flower in them. Large growing species (Table 2) if well fertilised and watered, will literally explode out of a pot and large sized plants are possible in a short time if conditions are ideal.
If the particular Agave suckers, then propagation is easy. Just summon some courage and remove an appropriate sized sucker with a sharp knife. You can dry this off for a couple of days or just pot it straight away. At least one species, the curious and desirable A. isthmensis produces axillary shoots, forming a small mound of heads. In this case it is necessary to dismember the clump to procure shoots