Mammillaria haageana CRESTED is a unique and visually striking form of the Mammillaria haageana cactus. The 'crested' or 'cristate' form is a mutation that causes the cactus to grow in a wavy, fan-like pattern rather than the typical spherical or cylindrical shape. This form is highly sought after by cactus collectors for its unusual appearance. Here's a detailed description and some cultivation tips:

Description:

1. Growth Habit: Instead of growing upright, the crested form grows laterally in a wavy, brain-like pattern. This makes each specimen unique.
2. Size: The size can vary, but generally, it remains compact, making it suitable for cultivation in smaller spaces or containers.
3. Stem: The stem is typically green, often obscured by spines and wool.
4. Spines: The spines are dense and can be white, yellow, or pinkish. They are arranged around the numerous areoles in a star-like pattern.
5. Flowers: Mammillaria haageana CRESTED produces small, bell-shaped flowers that are usually pink or red. The flowers emerge from the areoles at the top of the crest.
6. Fruit: The fruit is small and red, containing tiny seeds.

Cultivation Tips:

1. Lighting: Prefers bright, indirect sunlight. Direct sunlight can cause scorching, especially in hot climates.
2. Watering: Water moderately during the growing season (spring and summer) and sparingly in winter. Allow the soil to dry out completely between waterings.
3. Soil: Use a well-draining cactus mix. Mixing regular potting soil with sand or perlite can improve drainage.
4. Temperature: It prefers warm temperatures but should be protected from extreme heat and frost. Ideal growing temperatures are between 10°C to 30°C (50°F to 86°F).
5. Fertilizing: Fertilize lightly with a cactus-specific fertilizer during the growing season.
6. Repotting: Repot every 2-3 years or when the plant outgrows its pot. Handle carefully to avoid damaging the delicate crest.
7. Pests and Diseases: Watch out for common pests like mealybugs and scale insects. Good ventilation and proper watering can help prevent most diseases.

Mammillaria haageana CRESTED is an extraordinary and fascinating plant, ideal for collectors and enthusiasts who appreciate unique cacti forms.