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Plant Highlight: Agave victoriae-reginae
Taxonomic placement and area of occurrence
An article in in the journal Acta Botanica Mexicana in 2011 established the current classification of 3 species and one additional subspecies in the Agave victoriae-reginae complex, all of them native to northern Mexico. This complex is part of the section Heteracanthae within the genus Agave. The 3 species are Agave victoriae-reginae, Agave nickelsiae (sometimes grown under the synonym Agave ferdinandi-regis) and Agave pintilla (newly described in the 2011 article). The additional subspecies is Agave victoriae-reginae subsp. swobodae, applied to populations of Agave victoriae-reginae in southern Coahuila and northeastern Durango, where plants are smaller than at the species’ type locality. However, it is worth noting that in Agaves of Continental North America, H.S. Gentry’s classic work which was published in 1982, only Agave victoriae-reginae was recognized. Gentry treated A. nickelsiae (listed under the name Agave ferdinandi-regis) as a form of A. victoriae-reginae, and A. pintilla had not yet been described.
Of the three species in the complex, much the most abundant is A. victoriae-reginae, which occurs in great numbers in the mountains west of Monterey, in the state of Nuevo Leon. Populations are also found both to the north and to the south of Monterey. Limestone is a common rock type in this part of Mexico, and A. victoriae-reginae is generally found growing in cracks and ledges on limesone rocks rather than in soil.
About the plant
Plants of Agave victoriae-reginae have stemless or short-stemmed rosettes of triangular to lanceolate-triangular green leaves that are thick and fibrous, with dramatic white lines on the leaf faces, and they may be single-headed or produce a few offsets to make a small clump of heads. As agaves go, this is a compact species, with a rosette diameter on mature individuals of up to 2 feet (60 cm). The leaf length varies from 4 to 8.7 inches (10 to 22 cm), while the width is between 1.5 and 2 inches (3.7 to 5 cm). At the leaf tip is a sharp black spine (occasionally the main spine is accompanied by one or two smaller spines). The base of the spine arises from a horn-like white strip that extends down the leaf margins, and also down the keel that is usually present in the middle of the lower surface, extending part-way down the leaf. Sometimes there are additional white lines or dashes in the vicinity of the leaf tip, apart from the conspicuous white markings that indicate where the margins of adjacent leaves came in contact with the leaf as it formed at the plant’s growing tip.
Agave victoriae-reginae is a variable species, and numerous forms were named by Breitung in 1960, published in the Cactus and Succulent Journal. However, these names were applied to particular individual plants with unusual traits (such as having extra-wide leaves, extra-long and narrow leaves, extra-long end-spines, etc.), and while such differences are interesting to note, they are not worthy of taxonomic recognition as distinct forms. The name Agave victoriae-reginae subsp. swobodae, published by Halda in 2000, was applied to populations in southern Coahuila and westward into Durango, where plants are generally smaller and often make offsets. In this case, the name refers to differences in whole populations, not merely cherry-picked individuals. However, a smaller plant from the type locality which produces offsets could probaly not be told apart from its western relatives, so everyone does not agree that the differences rise to the level of a separate subspecies.
About the flowers and fruits
This is a relatively slow-growing species, often taking two decades or longer to reach maturity and produce an inflorescence. This timing is influenced by the conditions under which a plant is growing, so a plant with regular watering, especially if fertilizer is applied, will flower earlier than one grown hard or confined to a small pot. Flowering is in summer, with the stalk usually beginning to emerge in spring. At the Ruth Bancroft Garden, we have had plants open their first flowers in the latter half of June or in July, with flowering ending between late July and late August. The height of the inflorescence is up to 14 feet (4.3 m), with the flowers densely arranged along the upper half. The pedicels are very short, so that the flowers appear to emerge directly from the stalk. However, although they are sometimes single, they usually come in trios or pairs, and these are essentially much-reduced floral branches, so the inflorescence is not a true spike. Even so, the inflorescences of this and other members of Agave subgenus Littaea are often referred to as “spicate” because they do not have clusters of flowers held at the ends of obvious floral branches, as is seen in Agave subgenus Agave.
At the bud stage, the flowers of A. victoriae-reginae are off-white, often tinged with pale green or sometimes pale purple, with the base of the flower greener. When the flowers open, the six tepals* curl back to reveal the whiter or yellowish-white inside, with the six stamens and the central pistil extending well beyond the mouth of the flower. The yellow pollen on the large anthers held atop each stamen make the flowers look yellower from a distance than they actually are. Not including the protuding pistil and stamens, the flowers are between 1 and 1.8 inches long (25.5 to 38 mm).
When a flower is pollinated, the green basal portion swells to become a seed capsule, while the upper portion withers. The capsules are shaped like little rugby balls, or American footballs, with a length of .6 to .8 inch (15-21 mm). They blacken as they mature, eventually splitting along 3 lengthwise seams to release the black seeds. The seeds are stacked in 3 chambers within, and they are about .16 inch long (4 mm). As with other Agave species, the rosette will die after flowering, although offsets may continue to grow when these are present.
Plants in cultivation
Agave victoriae-reginae is not difficult to grow if given good drainage, plenty of sun and occasional water during its growing season (between spring and fall). It will tolerate wet spells in winter (its resting period) provided that there is good drainage, so that its roots do not become too waterlogged. Because the rosettes are so compact and formal-looking, this plant is often grown in pots, and it looks great in a situation such as a pair of urns on either side of a greenhouse entrance. It also makes a wonderful focal point in a garden bed or a rockery, amazing viewers when its lofty flower stalk emerges. Plants can grow happily in full sun or half-day sun, but with too much shade they may lose the compact form that makes them so attractive. This is a surprisingly cold tolerant species, surviving winter lows down to about 10° F (-12° C).
*The neutral term tepals is used for flowers that do not have distinct and differing sepals and petals.
