Hoya Callistophylla is a climbing or trailing epiphytic plant native to Borneo. This Hoya species stands out due to its long, narrow leaves that typically measure between 4-6 inches but can reach up to 10 inches in length. The leaves feature beautiful veining and under high light conditions, can take on a bronze colour. Its flowers are typical to many Hoyas, featuring small, star-shaped blossoms in clusters, usually creamy white or light yellow with a red or pink center.

Here's a detailed care guide for Hoya callistophylla:

1. Light: Hoya callistophylla prefers bright, indirect light. While it can tolerate a bit of direct morning or late afternoon sunlight, harsh midday sunlight can scorch the leaves, leading to discolouration or brown spots. An east or west-facing window that receives filtered light is ideal.

2. Water: Allow the top inch or so of the potting mix to dry out between waterings. Overwatering can lead to root rot, which can be fatal to the plant. On the other hand, Hoyas are quite drought-tolerant and can stand missing an occasional watering.

3. Soil: A well-draining, aerated potting mix is key. Consider a mix of one part perlite or pumice, one part orchid bark, and one part peat or coco coir. The aim is to mimic its natural epiphytic conditions where it would grow on trees with its roots exposed to air.

4. Temperature: Hoya callistophylla prefers warm temperatures and doesn't tolerate cold very well. Aim to keep the environment between 60-85°F (15-29°C). Protect it from drafts and sudden temperature changes.

5. Humidity: As a tropical plant, it thrives in a humid environment. Aim for a humidity level of around 40-60%. You can increase humidity by placing the plant on a tray with water and pebbles, grouping it with other plants, or using a room humidifier.

6. Fertilizer: Feed your Hoya callistophylla every 2-4 weeks during the growing season (spring to early fall) with a balanced houseplant fertilizer diluted to half the recommended strength. Reduce feeding during the winter months when the plant's growth slows.

7. Pruning: While Hoyas generally don't require much pruning, you can trim your plant to control its size and shape. Always prune just above a node (where a leaf joins the stem) and remember that the end of the stem is where new growth occurs.

8. Repotting: Hoyas prefer to be a bit root-bound and generally only need repotting every 2-3 years. When you do repot, choose a pot only slightly larger than the current one and make sure it has good drainage.

9. Propagation: Hoya callistophylla can be propagated through stem cuttings. Cut a healthy vine with at least one node, let it air dry for a day to let the cut end callous over, and then place in water or directly in soil to root.

Remember, every plant is unique, and its needs can slightly vary based on the environment (light, humidity, etc.). Pay attention to your plant's health and adjust your care routine as needed. Also, note that all parts of the Hoya are toxic if ingested, so it should be kept away from pets and small children.