Mammillaria elongata, also known as the Ladyfinger Cactus, is a popular cactus species often grown as a decorative plant due to its unique appearance and relatively easy care requirements. The "crest" form of Mammillaria elongata, sometimes called Mammillaria elongata var. cristata, exhibits a distinctive and intriguing growth pattern.

In the crest form, the cactus develops a wavy, contorted, or ribbed appearance, diverging from the standard cylindrical shape of the typical Mammillaria elongata. This unusual growth pattern is due to a genetic mutation or irregularity in the plant's growth process. The crest form can look quite striking, with the plant often forming a dense, irregular mass of clustered stems.

Care for a Mammillaria elongata crest involves similar principles to those for the standard form:
- **Light:** Provide bright, indirect sunlight. It can handle some direct sun, but too much can lead to sunburn.
- **Water:** Water sparingly. Allow the soil to dry out completely between waterings. Overwatering can lead to root rot.
- **Soil:** Use well-draining cactus or succulent soil.
- **Temperature:** It prefers temperatures between 65-80°F (18-27°C). It can tolerate brief periods of colder temperatures but should be protected from frost.

This cactus is also relatively low-maintenance and can add a unique visual interest to a collection.