Aloes and their close relatives are uniquely susceptible to the aloe mite, a contagious microscopic villain which lives inside the plant and announces its presence in the form of aloe cancer, a chronic and persistent disease. The distorted growth presents various ways, but it looks irregular and "wrong" and is often bubbly at the surface, with orange or yellow highlights. The best treatment of aloe mite is removal of the affected area by careful surgery, potentially including decapitation of affected stems. Consider removing the entire plant. Dispose of mite infested cuttings or plants very carefully, and sterilize instruments after use.
Zero tolerance is the best policy where aloe mites are locally present. Most ordinary pesticides (like the systemic insecticide imidacloprid) do not knock down aloe mites, which are closer genetically to spiders and spider mites than insects. Specialized miticides are available but they tend to be really expensive and require careful use. Chemical agents are not typically going to solve your aloe mite problem on their own, without some careful surgery first.
Some aloes are more susceptible to the aloe mite than others. By far the most common host in cultivation may be Aloe arborescens. Mites tend to show up most often on inflorescences, which give them a great platform for dispersal. Remove affected inflorescences at first sight and monitor the stem afterwards.
The Lomatophyllum group from Indian Ocean islands can be distinguished by a fleshy berry-like fruit, which differs from the usual dry, dehiscent (popping or splitting open) aloe fruit.
The grass aloes have thin, linear leaves and often bulbous bases. They are the least succulent, toothy, or substantial.
The maculate aloes have spotted leaves, relatively short stems, and flowers that are bulbous at the base. They can be particularly difficult to identify, even for experts.
Stemless aloes, a large group, may be solitary or grow in clumps. They are well represented in cultivation. One small stemless aloe (aristata) was recently moved to its own monotypic genus, Aristaloe.
The aloes which grow a stem include sprawling aloes, which tend to grow sideways, and shrubby aloes, which tend to form large, branching groups. The genus Aloiampelos was recently created for 7 related scrambling aloes, including the relatively common ciliaris and striatula.
Two aloes (plicatilis and haemanthifolia) make rounded, distichous leaves in a fan shape, and these were recently separated into the revived genus Kumara.
Three spotted aloes from Namibia have distinctive leaves with a V shape in crossection, and these were recently separated into the new genus Gonialoe.
Finally, tree aloes may grow up to 60 feet tall (the giant is A. barberae). They may be solitary and unbranched (the single-stemmed tree aloes) or branch, either at the base or at the crown. The tree aloes tend to make especially dramatic flowers. The genus Aloidendron was recently created for 6 related tree aloes, mostly on the large side.
It is generally unspotted, clumps freely, and reaches a larger size than the other common medicinal aloe in cultivation, Aloe officinalis (also known as Aloe vera chinensis), which can usually be distinguished by orange or coral flowers. Aloe vera gel is used for the topical relief of skin ailments, while Aloe officinalis is said to have benefits when consumed. In addition, Aloe ferox juice extract is promoted for various uses including as a laxative. Do not consume any aloe you cannot definitively identify as medicinal, which usually requires seeing the flowers. This is a diverse genus of many non-medicinal plants and even a few poisonous ones.
Open pollination in the aloe garden gives rise to all sorts of strange and interesting hybrids. Most species are quite promiscuous; a few may self-pollinate. Seed which is not produced carefully, excluding pollinators, is likely to be less than pure. Wait until the capsule dries up and breaks open to harvest mature seed (except with Lomatophyllum, which makes an indehiscent berry).
indehiscent: In botany, not popping or splitting open spontaneously when mature, as a capsule or an anther.
A recent reorganization of the aloes resulted in the splitting of a few species into the genera Kumara, Aloidendron, Aristaloe, Aloiampelos, and Gonialoe (details above), plus a few species absorbed from Chortolirion. At the same time Haworthia was split into three genera with the addition of Haworthiopsis and Tulista.