Mountain Aloe

Basic Information

Common Name: Mountain Aloe
Scientific Name: Aloe marlothii
Native Habitat: Southern Africa, including South Africa, Eswatini (Swaziland), Botswana, Zimbabwe, and Mozambique. It is commonly found in rocky outcrops, hillsides, grasslands, and bushveld, often in full sun and well-drained locations.

History / Discovery / Cultivator

Aloe marlothii, commonly known as the Mountain Aloe, is a striking and iconic plant of the Southern African landscape. While its use and recognition by indigenous peoples undoubtedly predates formal botanical study by centuries, the plant received its scientific name relatively recently in the context of botanical history. The species was formally described and named in honour of Rudolf Marloth (1855-1931), a distinguished German-born South African botanist, analytical chemist, and pharmacist. Marloth’s extensive work in documenting the flora of Southern Africa was monumental, culminating in his multi-volume magnum opus, “The Flora of South Africa.” It was fitting that such a prominent and widespread species was named in his honour, acknowledging his significant contributions to understanding the region’s biodiversity.The plant itself is a testament to the evolutionary pressures of its semi-arid native environment. As early European explorers and naturalists ventured into the diverse landscapes of Southern Africa, large, arborescent aloes like Aloe marlothii would have been impossible to overlook. Their commanding presence on hillsides and rocky outcrops made them a focal point of the flora. The process of formal scientific classification involved collecting specimens, detailed botanical descriptions, and comparative studies to distinguish it from other large aloe species, such as Aloe ferox. This work was part of the broader effort during the 18th, 19th, and early 20th centuries to catalogue the vast and unique plant life of the African continent.While not cultivated in the same way as agricultural crops or many ornamental garden plants for specific traits like colour or yield, Aloe marlothii has been utilized by local communities for various purposes, although specific traditional uses might vary and are less globally documented compared to Aloe vera. More significantly, its aesthetic appeal and resilience have made it a popular subject in horticulture and landscaping, particularly in arid and semi-arid regions globally that mimic its native conditions. Cultivation efforts focus primarily on propagation for ornamental purposes, appreciating its architectural form and dramatic flowering stalk. It has become a staple in xeriscaping and succulent gardens, valued for its low water requirements and imposing stature. Its natural distribution across a wide geographical area suggests it has long been a visible and integral part of the ecosystems and human cultures within its range, with Rudolf Marloth’s naming providing its official recognition within the global scientific framework. The plant’s resilience and adaptability have facilitated its popularity beyond its native range, solidifying its place as a significant species both ecologically and horticulturally.

Plant Care Summary

Category	General Requirement	Notes
Light	Full Sun	Requires bright, direct sunlight for best growth and flowering. Can tolerate some afternoon shade.
Water	Infrequent	Drought tolerant. Allow soil to dry out completely between deep waterings. Less water in winter.
Humidity	Low	Thrives in low humidity conditions. Avoid high humidity environments.
Temp. Range	Warm/Moderate	Tolerates light frost (briefly down to -5°C/23°F) but prefers warmer climates. Protect from hard freezes.
Soil Type	Well-draining	Use a succulent or cactus mix, or blend potting soil with coarse sand or perlite for drainage.
Fertilizer	Infrequent	Feed sparingly in spring and summer with a diluted balanced or succulent-specific fertilizer.
Toxicity	Mildly Toxic	Contains anthraquinones. Can cause gastrointestinal upset if ingested; sap may cause skin irritation.

Botanical Insights

Adaptations

Aloe marlothii is exceptionally well-adapted to surviving in the often harsh, arid or semi-arid conditions of Southern Africa. Its most obvious adaptation is its succulence: thick, fleshy leaves store significant amounts of water, allowing the plant to endure long periods of drought. The leaves are covered with a waxy cuticle which helps minimize water loss through evaporation. The robust, spiny margins and surfaces of the leaves likely serve as a deterrent to grazing animals. The plant’s growth form, often developing a single, thick stem over many years, elevates the rosette, potentially protecting it from ground-level herbivores and improving air circulation. The inflorescence is a spectacular, branched structure, typically with multiple upright racemes of flowers, designed to attract pollinators like birds (sunbirds) and insects. This ensures successful reproduction even in spread-out populations. Its root system is adapted to capture scarce water resources, possibly developing both deep roots for stability and accessing deeper water sources and shallow roots to absorb surface moisture during infrequent rain events.

Propagation Methods

Propagation of Aloe marlothii is primarily and most reliably achieved through seed. Mature plants produce abundant seed from their striking inflorescences if successfully pollinated. Seeds should be sown in a well-draining succulent mix in warm conditions. Germination can be variable but is generally successful with fresh seed. Unlike many clumping aloe species, mature Aloe marlothii typically forms a single stem and does not readily produce offsets (pups) from the base. While large stem cuttings might theoretically be attempted from younger plants or multi-headed specimens (which are less common), this is not a standard or easy method for this species due to its growth habit and size. Division is not applicable to mature, single-stemmed plants. Therefore, propagation from seed remains the most practical and common method for Aloe marlothii.

Toxicology

Like many Aloe species, Aloe marlothii contains compounds within its leaf sap that can be toxic if ingested. The primary active compounds are anthraquinones, such as aloin, which are concentrated in the bitter yellow latex layer just beneath the epidermis of the leaves. If humans or pets (cats, dogs) ingest significant quantities of this sap, it can cause gastrointestinal distress. Symptoms may include vomiting, diarrhea, abdominal pain, and lethargy. The cathartic effect of anthraquinones is well-known. Additionally, contact with the sap can sometimes cause skin irritation or dermatitis in sensitive individuals or animals. While generally considered to have low to moderate toxicity compared to plants containing potent cardiotoxins or neurotoxins, ingestion is not advised, and symptomatic treatment may be required for pets that consume large amounts. The plant is typically considered safer than plants containing cardiac glycosides or oxalates but can still cause significant digestive upset.

Common Problems

Pests:

• Mealybugs: Small, white, cottony insects that cluster in leaf axils and on roots.
• Scale Insects: Small, hard-shelled or soft-bodied insects that attach to stems and leaves, sucking sap.
• Aphids: Small, soft-bodied insects that cluster on new growth and flower stalks.
• Aloe Mites (e.g., Aloe Gall Mite): Microscopic mites that cause distorted, tumor-like growths (galls) on leaves and flower stalks. This is a particularly serious pest for aloes.

Diseases:

• Root Rot: Caused by overwatering and poor drainage, leading to mushy, black roots and stem base.
• Fungal Leaf Spots: Various fungi can cause spots or lesions on leaves, often exacerbated by high humidity or water sitting on leaves.
• Rust: Fungal disease appearing as rusty-coloured spots or pustules on leaves.

Other:

• Etiolation: Stretched, pale growth with widely spaced leaves caused by insufficient light.
• Sunburn: Brown or black scorched patches on leaves if moved suddenly into intense sun or exposed to extreme heat.
• Failure to Flower: Often due to insufficient light, lack of maturity (plants need to be several years old), or lack of necessary temperature fluctuations.
• Frost Damage: Leaves turn mushy and black after exposure to hard freezes.

Rarity & Value

Rarity:

Aloe marlothii is not considered rare in its native habitat across Southern Africa; it is a widespread and common species. However, well-grown, mature specimens, particularly those with a substantial trunk and large rosette, can be less commonly available in cultivation simply because they take many years to reach such a size. While propagation from seed is straightforward, the time required to grow a plant from a seedling to a large, landscape-sized specimen contributes to the higher value and relative ‘rarity’ of mature individuals in the horticultural trade outside their native range. Specific forms or any rare natural variegation would be exceptionally rare and highly sought after by collectors.

Value:

The market value of Aloe marlothii is significantly influenced by its size and age. Small seedlings or young plants are relatively inexpensive. As the plant grows and develops its characteristic trunk and large rosette, its value increases considerably. Large, mature specimens suitable for landscape focal points command the highest prices due to the many years of growth they represent and the cost/difficulty of transport. Other factors affecting value include the overall health and condition of the plant, the quality of its form (a straight, well-developed trunk and symmetrical rosette are desirable), and provenance (whether it was nursery grown or potentially wild-collected, which can impact legality and ethical considerations). Current trends in succulent popularity and regional availability also play a role. Variegated forms, if they exist and are stable, would be exceptionally valuable in the collector’s market.