🇲🇲 Habitat and Ecology
Holcoglossum clausum is a recently described (2024), rare monopodial epiphytic or lithophytic orchid. It is native to the Indo-Myanmar biodiversity hotspot, specifically recorded in Myanmar (Southern Shan State) and Thailand (Doi Inthanon). It thrives in tropical mixed deciduous forests situated on limestone formations at elevations of approximately 1,500 to 1,600 metres. This specific habitat indicates a preference for cool-intermediate conditions, distinct seasonality, and excellent drainage provided by the limestone substrate.
🌸 Description and Distinguishing Features
This species is a pendent, epiphytic herb distinguished by its graceful habit and unique floral structure.
Foliage: The plant features a short stem carrying long, slender, subterete (almost cylindrical) leaves that can reach up to 45 cm in length. The leaves are channelled on the ventral side and are pendent, draping downwards from the host.
Flowers: The flowers are borne on horizontal to arching racemes. The blooms are typically pink.
Aesthetics: The defining feature, referenced by the specific epithet clausum (Latin for 'closed'), is that the flowers barely open, retaining a cup-like or closed appearance compared to other members of the genus. The lip has a long spur (approx. 1.3 cm).
Differentiation: H. clausum is part of a complex group of terete-leaved Holcoglossums but can be identified by specific traits:
Versus H. semiteretifolium: H. semiteretifolium has an upright growth habit and significantly shorter leaves (approx. 15 cm), whereas H. clausum is pendent with very long leaves (up to 45 cm) and a longer spur.
Versus H. himalaicum: While allied, H. clausum differs in petal size (larger, 7-8 mm vs 4-5 mm) and has a shorter stem compared to the often elongated stem of H. himalaicum.
💧 Cultivation and Care
Holcoglossum clausum requires conditions that mimic its high-elevation, limestone forest habitat.
Light: Needs bright, filtered light. As a terete-leaved species, it can tolerate higher light levels than broad-leaved orchids, but protect from scorching midday sun.
Substrate: Best grown mounted on cork bark or in hanging baskets to accommodate its pendent leaves and need for rapid drainage. Adding limestone chips to the mix or using a calcium-rich fertilizer may be beneficial given its natural calcicolous habitat.
Watering: Water regularly and copiously during the active growing season, allowing roots to dry quickly. Reduce watering significantly in winter, providing a cool, drier rest to stimulate flowering.
Temperature:
Optimal Daytime Temperature: 20-25 C (68-75 F).
Optimal Nighttime Temperature: A cool drop is essential, ideally 10-15 C (50-59 F), reflecting its montane origin.
Humidity: High humidity (70-80%) with excellent air movement is critical.
✨ Unique Features
Holcoglossum clausum is a botanical novelty, only formally described in 2024. It is prized by collectors for its dramatic, long pendent foliage and its curious "closed" pink flowers that offer a distinct morphological variation within the Holcoglossum alliance.
🏷️ Specifications
Plant Size: Recently deflasked by us in the UK. Plants are about 2 years from flowering size
Plant Family: Orchidaceae
Plant Passport: A Holcoglossum clausum B 140084 C [buyer to use number of the plant label] D GB
