Croton myriaster

Croton myriaster
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Embryophytes
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Malpighiales
Family: Euphorbiaceae
Genus: Croton
Species:
C. myriaster
Binomial name
Croton myriaster
Baker
Synonyms[2]
  • Croton calomeris Baill.
  • Croton myriaster var. austromadecassus Leandri
  • Croton regeneratrix var. ranomafanae Radcl.-Sm.

Croton myriaster is a species of flowering small tree or shrub in the spurge family, Euphorbiaceae. It is endemic to Madagascar, where it occurs primarily in humid and subhumid montane forests.

Croton myriaster was first described by John Gilbert Baker in 1882[3][4] and has since been included in several taxonomic treatments of Euphorbiaceae and Malagasy flora, with three later names now treated as synonyms.

It is known for having medicinal uses and is listed in the World Checklist of Useful Plant Species 2020.[5] It has been assessed as Near Threatened on the IUCN Red List due to ongoing habitat loss of Madagascar's humid forests.[1]

Description

Croton myriaster grows to around 10 metres (33 ft) tall, with stems up to 20 centimetres (7.9 in) in diameter.[6] Young twigs are covered in short, stellate (star-shaped), hair-like appendages (trichomes), which are widespread within the genus. These trichomes are known to help protect against abiotic stresses, herbivores, and pathogens.[7]

The leaves are simple and arranged alternately along the stems. Leaf blades are ovate to lanceolate, typically 8–15 cm long, with a rounded base, a pointed tip, and entire or finely toothed margins. The leaf stalk (petiole), measures about 1.5–2.5 cm in length. The lower leaf surface is paler and whitish, often with fine hairs. At the base of the leaf blade are two small brown extrafloral nectary glands[6], which are a characteristic feature of some members of the Euphorbiaceae family.[8]

Croton myriaster is monoecious, with separate male and female flowers on the same plant. The flowers are arranged in a short, upright cluster called a raceme, at the end of a densely hairy axis.[3] Within each inflorescence, multiple male flowers occur towards the tip, with just two or three female flowers near the base. Flowers are unisexual, small, and white to pale green or yellow, with five floral parts, and the petals are greatly reduced.[6] Male flowers have a bell-shaped calyx, five small petals, and 12–16 free stamens. Female flowers have softly hairy, brownish sepals and no petals, a three-lobed ovary, and three branched styles. The flower stalk elongates as the fruit develops.[6]

After flowering, the plant produces a hard, three-lobed capsule, typical of the spurge family.[8] The capsule is reddish-brown, about 12 mm long, and covered with fine glandular hairs. Each fruit contains three seeds, which are oval, approximately 7 mm long and grooved.[6]

Etymology

Croton derives from the Greek κρότων (krótos), meaning "tick", referring to the tick-like appearance of the seeds in some species.[9] The species name, myriaster is formed from Greek roots: myri- (from μύριοι, meaning "countless" or "many")[10] and -aster (from ἀστήρ, meaning "star").[11] The name may refer to the star-like stellate trichomes characteristic of the species.

The gender of the Greek Croton (κρότων) is masculine, although it has been historically treated as neuter or feminine. This has required correction within the genus of epithets with non-masculine endings.[12] The epithet myriaster is already masculine and was therefore not subject to any correction.

Habitat and ecology

Croton myriaster occurs in humid and subhumid montane forest in Madagascar at elevations of approximately 800–1,700 m (2,600–5,600 ft).[1] The humid and subhumid bioclimatic zones cover the eastern and central plateaus of Madagascar. These forests are characterised by high annual rainfall (about 1,500–2,400 mm (59–94 in)), a short or absent dry season, and predominantly evergreen vegetation. At higher altitudes, frequent cloud condensation compensates for reduced rainfall. They typically have a closed, multi-layered canopy and a dense understorey, with canopy height declining with increasing elevation.[13] Tree diversity is high, and members of Euphorbiaceae, including Croton, are among several understory and mid-layer trees and shrubs that are dominant within these ecosystems. Other common families include Annonaceae, Apocynaceae, Melastomataceae, Rubiaceae, and Sapindaceae.[13]

Extrafloral nectary glands

Croton myriaster has nectary glands at the base of the leaves, a feature that is common in the Croton genus.[14] These nectar-secreting structures found outside the flowers are not involved directly in pollination. In studies of other Croton species, they have been found to be associated with mutualistic interactions, such as contributing to defense against herbivores.[14]

Distribution

Croton myriaster is endemic to Madagascar and is one of the few Malagasy Croton species that is widespread across the island,[12] having been recorded in all six former provinces: Antananarivo, Antsiranana, Fianarantsoa, Mahajanga, Toamasina, and Toliara.[15] The species is known from 208 preserved specimens, with occurrences spanning from the North to the South of the country and with concentration in the humid to subhumid eastern and central regions.[2] There are 15 subpopulations across 11 locations, and the total area within which the species is known to occur is approximately 41,800 km2 (16,100 sq mi).[1]

Taxonomy and systematics

Croton myriaster is a member of the spurge family, Euphorbiaceae. The Croton genus comprises more than 1,200 species worldwide,[16] with ~114 of the roughly 450 described Old World species occurring in Madagascar.[12]

Croton is divided into four monophyletic subgenera: subg. Quadrilobi, subg. Adenophylli, subg. Geiseleria, and subg. Croton L.[17] Three of these are restricted to the Neotropics, while the fourth, subgenus Croton, comprises all paleotropical species. All Malagasy species, including C. myriaster, belong to this Old World clade, which is inferred to have originated from the New World, followed by diversification in Africa and the western Indian Ocean region (WIOR).[18]

Early classifications of Croton within Madagascar grouped some Malagasy species with New World species. Subsequent molecular analyses have shown that several of these groupings didn't reflect true evolutionary relationships, which has led to revisions of the genus. Phylogenetic analyses place Croton myriaster within the Adenophorus group.[18] Within this revised grouping, C. myriaster is most closely related to C. regeneratrix.

Morphological classification

Trichome morphology, distribution and density are widely used for taxonomic purposes in the Croton genus, although inconsistent terminology in earlier work limited their use.[7] A recent revision by Pinto-Silva et al. of trichome classification within the genus aimed to improve clarity in how these characters are described and used in species identification. The Adenophorus group are characterised by stellate (star-like) trichomes, which, together with other diagnostic features such as nectary glands and tightly clustered flower inflorescences, help to distinguish this lineage morphologically.[18]

Synonyms

The currently accepted name is Croton myriaster Baker, first published in the Journal of Botany v. 20, 1882.[19] Several names previously applied to Malagasy specimens are now treated as heterotypic synonyms,[20] including:

  • Croton calomeris Baill. in Bull. Mens. Soc. Linn. Paris 2: 860 (1890)
  • Croton myriaster var. austromadecassus Leandri in Ann. Mus. Colon. Marseille, sér. 5, 7(1): 58 (1939)
  • Croton regeneratrix var. ranomafanae Radcl.-Sm. in Gen. Croton Madag. Comoro: 202 (2016)

Croton regeneratrix var. ranomafanae Radcl.-Sm. (2016) is one of numerous Croton taxa described by Radcliffe-Smith (2016)[21] that were later placed into synonymy following reassessment.[12]

Uses

Croton myriaster has recorded traditional medicinal uses. A decoction prepared from the aerial parts is administered to children for epileptic attacks, and inhalations are used in the treatment of headaches. Croton myriaster is considered morphologically close to several other Malagasy medicinal species within the genus, with almost 40 Croton species from Madagascar being used in medicine. The wood is also known to be used as firewood.[6]

Phytochemistry

The bark contains trace amounts of alkaloids, although none have been detected in the leaves.[6]

Threats and conservation

Croton myriaster was assessed for the IUCN Red List of Threatened Species in 2020 and classified as Near Threatened under criterion B2ab(iii). No species-specific threats are identified, however, its primary habitat is subject to continuing decline in area and quality,[1] with 33.4% of Madagascar's humid forest's having been removed since the 1970s.[13] C. myriaster is known to occur in some protected areas, including Ranomafana National Park and Andringitra National Park.[15] Much of the protected area coverage within Madagascar's humid forest region lies above 500 m elevation[13], which broadly overlaps with the known elevational range of C. myriaster.

References

  1. 1 2 3 4 5 Ravololomanana, N. (2020). "Croton myriaster". IUCN Red List of Threatened Species. 2020 e.T167037682A167208514. doi:10.2305/IUCN.UK.2020-3.RLTS.T167037682A167208514.en. Retrieved 19 May 2026.
  2. 1 2 "Croton myriaster Baker". Global Biodiversity Information Facility. Retrieved 19 May 2026.
  3. 1 2 Gilbert, Baker, John (1882). "Contributions to the flora of central Madagascar". Journal of Botany, British and Foreign. 20. Archived from the original on 15 September 2024.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ↑ "Croton myriaster". International Plant Names Index (IPNI). Royal Botanic Gardens, Kew. Retrieved 17 May 2026.
  5. ↑ Diazgranados, M. (2020). World Checklist of Useful Plant Species. Royal Botanic Gardens, Kew. p. 473.
  6. 1 2 3 4 5 6 7 Schmelzer, G. H. (2008). Medicinal plants. Plant Resources of Tropical Africa. The Netherlands: PROTA Foundation. p. 209.
  7. 1 2 Pinto-Silva, Natânia Pereira; De Souza, Katiúscia Freire; Marques Silva, Otávio Luis; Vitarelli, Narah Costa; Da Paixão Noronha Pereira, Amanda; Soares, Deborah Aragão; Sodré, Rodolfo Carneiro; Medeiros, Débora; Caruzo, Maria Beatriz Rossi; Carneiro Torres, Daniela Santos; Da Silva, Marcos José; Meira, Renata Maria Strozi Alves; Riina, Ricarda; Feio, Ana Carla (2023-09-01). "Trichomes in the megadiverse genus Croton (Euphorbiaceae): a revised classification, identification parameters and standardized terminology". Botanical Journal of the Linnean Society. 203 (1): 37–49. doi:10.1093/botlinnean/boad008. hdl:10261/364405. ISSN 0024-4074.
  8. 1 2 Judd, W. S. (1999). Plant systematics: a phylogenetic approach. Sunderland, MA: Sinauer Associates. p. 271.
  9. ↑ Gledhill, D. (2008). The Names of Plants. Cambridge: Cambridge University Press. p. 126.
  10. ↑ Gledhill, D. (2008). The Names of Plants. Cambridge: Cambridge University Press. p. 267.
  11. ↑ Quattrocchi, U. (1999). CRC World Dictionary of Plant Names: Common Names, Scientific Names, Eponyms, Synonyms, and Etymology. CRC Press. p. 220.
  12. 1 2 3 4 Berry, Paul E.; Kainulainen, Kent; Ee, Benjamin W. van (2017-11-15). "A Nomenclator of Croton (Euphorbiaceae) in Madagascar, the Comoros Archipelago, and the Mascarene Islands". PhytoKeys (90): 1–87. Bibcode:2017PhytK..90....1B. doi:10.3897/phytokeys.90.20586. ISSN 1314-2003. PMC 5784240. PMID 29391851.
  13. 1 2 3 4 Moat, J. (2007). Atlas of the vegetation of Madagascar. Royal Botanic Gardens, Kew. pp. 31–32.
  14. 1 2 Vitarelli, Narah C.; Riina, Ricarda; Caruzo, Maria Beatriz R.; Cordeiro, Inês; Fuertes-Aguilar, Javier; Meira, Renata M. S. A. (June 2015). "Foliar secretory structures in Crotoneae (Euphorbiaceae): Diversity, anatomy, and evolutionary significance". American Journal of Botany. 102 (6): 833–847. Bibcode:2015AmJB..102..833V. doi:10.3732/ajb.1500017. hdl:10261/169162. ISSN 0002-9122. PMID 26101410.
  15. 1 2 "Catalogue of the Plants of Madagascar". Tropicos. Retrieved 2 February 2026.
  16. ↑ Berry, Paul E.; Hipp, Andrew L.; Wurdack, Kenneth J.; Van Ee, Benjamin; Riina, Ricarda (September 2005). "Molecular phylogenetics of the giant genus Croton and tribe Crotoneae (Euphorbiaceae sensu stricto) using ITS and TRNL-TRNF DNA sequence data". American Journal of Botany. 92 (9): 1520–1534. doi:10.3732/ajb.92.9.1520. ISSN 0002-9122. PMID 21646170.
  17. ↑ Thaowetsuwan, Pakkapol; Ritchie, Stuart; Riina, Ricarda; Ronse De Craene, Louis (2020-08-04). "Divergent Developmental Pathways Among Staminate and Pistillate Flowers of Some Unusual Croton (Euphorbiaceae)". Frontiers in Ecology and Evolution. 8 253. Bibcode:2020FrEEv...8..253T. doi:10.3389/fevo.2020.00253. hdl:10261/271920. ISSN 2296-701X.
  18. 1 2 3 Haber, Elizabeth A.; Kainulainen, Kent; Van Ee, Benjamin W.; Oyserman, Ben O.; Berry, Paul E. (2017-04-01). "Phylogenetic relationships of a major diversification of Croton (Euphorbiaceae) in the western Indian Ocean region". Botanical Journal of the Linnean Society. 183 (4): 532–544. doi:10.1093/botlinnean/box004. ISSN 0024-4074.
  19. ↑ "Croton myriaster | International Plant Names Index". ipni.org. Retrieved 2026-05-17.
  20. ↑ "Croton myriaster Baker | Plants of the World Online | Kew Science". Plants of the World Online. Retrieved 2026-05-17.
  21. ↑ Radcliffe-Smith, A. (2016). The genus Croton in Madagascar and the Comoro Islands. Royal Botanic Gardens, Kew.
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