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Aloe castilloniae (2023)

Photo
Flowers on the textured-leaf form. Photo from Plantemania, https://plantemania.net/gb/.

By Emily Hall (December 2023)

At this year’s annual picnic, I had the lucky chance to select a charming, three-headed Aloe castilloniae from the attendance prize plant display. I had no idea that this species is a rare and highly sought-after specimen amongst aloe collectors!

It was described relatively recently in 2006 by French botanist, chemist, mathematician, explorer and author Jean-Benard Castillon, who named it in honor of his wife, Bernadette Castillon, a horticulturist specializing in Madagascan succulents. The newness of the species, its limited number of clone types and its slow growth habit have contributed to the demand for this plant.

Aloe castilloniae originates from an extremely dry stretch of southwestern Madagascar called the Plateau Mahafaly, where it is found growing a few miles inland on the coastal face of porous, calcareous (containing calcium carbonate) sandstone cliffs. It grows in a series of tightly stacked rosettes, and because its stems are not strong enough to hold the plant upright to any great height, it spreads in a sprawling, vinelike, heavily branching habit along the rocky ground.

The species forms clumps up to several feet wide, drooping over boulders and hanging off the face of cliffs at 330 to 980 feet above sea level. The stems can eventually grow up to 3 feet long, making it a likely specimen for a hanging pot as it matures.

There are two forms of A. castilloniae: the smooth-leaved (the type I received) and the textured-leaved, which has tubercules on the top or undersides of the leaves. The rigid, triangular, recurved leaves can be bluish-green to a deep olive green with prominent red teeth on the edges. In the textured form, the tubercules are also red, making a striking contrast against the green leaves. The textured form is currently more common in captivity, as propagation by tissue culture has made it more readily available than the smooth-leaved form.

The inflorescences of A. castilloniae are small, but attractive. Nearly 1 inch long, the tube-shaped flowers appear primarily from February to May (although they can appear throughout the year), shooting out on a 2-inch stem from the center of the leaf rosettes. The flowers are a bright red-orange with a yellowish tinge near the mouth.

This plant can be propagated easily by seed or by stem cuttings. Happily, no part of it is toxic for people or pets, making it an excellent house plant.

In cultivation, A. castilloniae likes bright, indirect light when indoors. While sun- and drought-tolerant, it does better in dappled shade outdoors and has a particular need for shade in late afternoon. It is not very heat tolerant and will go somewhat dormant in prolonged heat. In heavy sun, the leaves turn from green to a rusty burnt orange.

Although it can withstand a wider range, this aloe’s preferred temperatures are 50 to 85 degrees F, which reflect, of course, the normal temperature range of its native habitat. It is not winter-hardy but can survive temps as low as 25 degrees F if dry. Most sources state that it is intolerant of frost, but one commercial grower notes that it has endured light frost in outdoor plantings. In a mild climate, it would be happy outside in a well-drained, partially shaded rock garden or as a ground cover in a dry, quick-draining, sloped area.

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Smooth-leaf form. When the leaves are this sharply curved back, the plant could use water, but I’m increasing the water very gradually until the root structure is more developed. Photo by Emily Hall.

I will be interested to find if this plant fares well enough in the sometimes-extreme heat and humidity of our summers and the cool overnight temperature dips of our spring and fall to be kept outdoors and only brought in for the winter. One grower in the San Diego area stated that A. castilloniae specimens endure temperatures in the 90s and 100s. While this aloe may survive outside in our area’s climate, it may better thrive as primarily an indoor plant. Another source noted that it requires ample air flow, so a position near a fan would be optimal.

When kept within its preferred temperatures, fall and winter comprise A. castilloniae’s primary growth season. This makes the plant an especially welcome addition to a Midwestern succulent collection during the dreary winters, when many of our other plants are dormant.

Like most succulents, A. castilloniae needs a porous, well-drained, gritty mix; light fertilization in spring and summer; and repotting into a slightly larger container in spring every few years or when the roots emerge from the drainage holes. Because of the calcareous nature of its native soil, I’m going to research planting media that contain calcium carbonate for next spring’s repotting.

Although it can tolerate drought conditions, this aloe prefers regular watering. The soil should dry mostly between waterings, and no standing water should be allowed to settle in the rosettes.

I thank the club for giving me the opportunity to collect and learn about this rare and interesting plant that I otherwise never would have known about!

Sources:

Aloes in Wonderlandhttps://www.aloesinwonderland.com/plant-gallery/aloe-castilloniae
Llifle Encyclopedia of Succulentshttp://www.llifle.com/Encyclopedia/SUCCULENTS/Family/Aloaceae/29329/Aloe_castilloniae
San Marcos Growershttps://www.smgrowers.com/products/plants/plantdisplay.asp?plant_id=4256
T-Rex Plantshttps://trexplants.com/blog/care-diary-how-to-grow-aloe-castilloniae
Wikipediahttps://en.wikipedia.org/wiki/Aloe_castilloniae
World of Succulentshttps://worldofsucculents.com/aloe-castilloniae/