Angraecum costatum

Angraecum costatum Frapp. ex Cordem. is a small-flowered orchid accepted by Plants of the World Online, with a native range given as Réunion and a life form described as an epiphytic or lithophytic chamaephyte in the wet tropical biome [1]. It is not a large-flowered species: IOSPE records green flowers 5–6 mm across and places the plant among cool-growing epiphytes from 1,200–1,800 m [2]. The cultivated evidence available for this profile is narrow, consisting mainly of the cool-growing and semi-shade labels in IOSPE; watering, humidity, feeding, and repotting are not documented for the species in the supplied sources.

Names and Taxonomy

The accepted scientific name is Angraecum costatum Frapp. ex Cordem., first published in Fl. Réunion: 211 (1895) [1]. POWO accepts the species and lists nine synonyms [1]. The homotypic synonyms include Lemurangis costata (Frapp. ex Cordem.) Szlach., Mytnik & Grochocka, Macroplectrum costatum (Frapp. ex Cordem.) Finet, and Mystacidium costatum (Frapp. ex Cordem.) Cordem. [1]. Heterotypic synonyms include Angraecum longinode Frapp. ex Cordem. and Angraecum pseudopetiolatum Frapp. ex Cordem., with combinations in Lemurangis and Mystacidium [1]. These names should be treated as synonyms under the POWO treatment, not as separate species in a profile of A. costatum.

IOSPE places the species in section Lemurangis [2]. That sectional placement is an identification aid from a horticultural encyclopedia, not a substitute for the accepted-name decision in POWO. Documented common names are The Ribbed Angraecum in IOSPE [2] and Angrec côtelé in French in TaxRef [3]. TaxRef treats the species as endemic to Réunion [3], while POWO gives the native range as Réunion only [1]. IOSPE additionally reports Mauritius [2]; because POWO does not list Mauritius, that part of the IOSPE range should be regarded as an unresolved source disagreement rather than an established native record.

How to Identify This Species

POWO describes A. costatum as an epiphytic or lithophytic chamaephyte [1]. IOSPE describes a medium-sized, cool-growing epiphyte with an erect, simple or branched stem [2]. The leaves are borne in two ranks on the upper part of the stem; IOSPE describes them as bright green, lanceolate, and unequally bilobed at the apex [2]. This combination of a monopodial, leafy stem and small green flowers is useful for orientation, but the supplied evidence does not provide root dimensions, mature plant height, or leaf measurements.

The inflorescences are axillary and short-peduncled. IOSPE reports one or two axillary inflorescences, usually with two flowers, although one flower does not develop [2]. The flowers are green and 5–6 mm across [2]. The lip, spur, column, fragrance, and flower longevity are not documented in the supplied sources. Identification from a photograph or a nursery label alone is therefore weak: a confident determination should rest on flower structure and vegetative characters, and on comparison with the synonymy above. No documented look-alike comparison was available for this profile.

Native Range and Habitat

POWO gives the native range as Réunion and records the species in the wet tropical biome [1]. TaxRef also treats it as endemic to Réunion [3]. IOSPE reports it from Réunion and Mauritius in semi-shade at elevations of 1,200–1,800 m, growing as an epiphyte [2]. The Mauritius part of that statement conflicts with POWO and is not confirmed by the accepted-name source used here. The elevation range is likewise from IOSPE; POWO does not provide an elevation in the supplied excerpt.

Within its native range, the documented growth substrates are epiphytic and lithophytic [1]. IOSPE describes it as an epiphyte in semi-shade [2]. Host tree identity, lithological substrate, rainfall seasonality, and microhabitat details are not documented in the supplied sources. Native occurrence should not be confused with cultivated occurrence in orchid collections.

Species-Specific Care

The care evidence for A. costatum is limited. The table separates what is documented for the species from factors for which the supplied sources give no species-specific guidance. Native elevation is included only as habitat context, not as a greenhouse setpoint.

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The only species-specific cultivation labels in the supplied evidence are cool-growing and semi-shade [2]. Those labels are useful starting points but do not define a complete culture regime. A grower should not convert the 1,200–1,800 m native elevation directly into a day or night temperature, and should not assume the high humidity or heavy watering recommended for some larger, lower-elevation Angraecum species. The IOSPE entry is a compiled species encyclopedia rather than a controlled cultivation trial, so its cool-growing and semi-shade labels should be treated as reported horticultural guidance. No species-specific watering, humidity, feeding, or repotting data were available in the supplied sources.

Flowering and Pollination

IOSPE reports that A. costatum blooms in fall on one or two axillary inflorescences, usually with two flowers, one of which does not develop [2]. The flowers are small and green, 5–6 mm across [2]. The same source does not specify whether the flowering season refers to the Northern Hemisphere, the Southern Hemisphere, or a particular cultivation context; Réunion lies in the Southern Hemisphere, so the calendar meaning of fall should not be assumed without local confirmation.

Flower longevity, fragrance timing, nectar spur dimensions, and pollination are not documented in the supplied sources. The small green flowers and the genus Angraecum are sometimes associated with moth pollination in general orchid literature, but no pollinator observation or pollination study for A. costatum was supplied. A moth-pollination hypothesis based on flower shape should therefore be labeled as inference, not as a documented fact for this species.

Conservation and Responsible Cultivation

No formal conservation assessment for A. costatum was available in the supplied sources. POWO accepts the name and gives Réunion as the native range [1]; TaxRef treats it as endemic to Réunion [3]. Those are distribution and endemicity statements, not conservation status categories. No legal trade status or collection guidance specific to this species was documented in the supplied evidence, so no compliance claim should be inferred from a nursery listing alone.

Evidence and Limitations

This profile is based on supplied search snippets and page excerpts, not on a full taxonomic revision, herbarium examination, or controlled cultivation trial. The main material gaps are root and plant-size data, leaf dimensions, lip and spur morphology, fragrance, flower longevity, pollinator observations, and species-specific watering, humidity, feeding, and repotting guidance. The native range also has a source conflict: POWO lists Réunion only [1], while IOSPE adds Mauritius [2]. The IOSPE elevation and flowering statements are single-source horticultural reports [2]. The name status is well supported by POWO [1], but this draft has not been botanically reviewed and should not be treated as a verified publication-ready account.