Euphorbia stygiana

Life-forms

Classification System: APG IV

Superregnum: Eukaryota
Regnum: Plantae
Cladus: Angiosperms
Cladus: Eudicots
Cladus: Core eudicots
Cladus: Rosids
Cladus: Eurosids I
Ordo: Malpighiales

Familia: Euphorbiaceae
Subfamilia: Euphorbioideae
Tribus: Euphorbieae
Subtribus: Euphorbiinae
Genus: Euphorbia
Subgenus: E. subg. Esula
Sectio: E. sect. Helioscopia
Species: Euphorbia stygiana
Name

Euphorbia stygiana H.C.Watson, London J. Bot. 3: 605 (1844).
Synonyms

Homotypic
Tithymalus stygianus (H.C.Watson) Soják, Cas. Nár. Mus., Odd. Prír. 140: 176 (1972).

Distribution
Native distribution areas:

Continental: Africa
Regional: Macaronesia
Azores

References: Brummitt, R.K. 2001. TDWG – World Geographical Scheme for Recording Plant Distributions, 2nd Edition
References
Primary references

Watson, H.C., 1844. The London Journal of Botany 3: 605.

Links

Govaerts, R. et al. 2020. Euphorbia stygiana in World Checklist of Selected Plant Families. The Board of Trustees of the Royal Botanic Gardens, Kew. Published online. Accessed: 2020 Jul 12. Reference page.
International Plant Names Index. 2020. Euphorbia stygiana. Published online. Accessed: Jul 12 2020.
Govaerts, R. et al. 2020. Euphorbia stygiana in Kew Science Plants of the World online. The Board of Trustees of the Royal Botanic Gardens, Kew. Published online. Accessed: 2020 Jul 12. Reference page.
Tropicos.org 2020. Euphorbia stygiana. Missouri Botanical Garden. Published online. Accessed: 12 Jul 2020.
IUCN: Euphorbia stygiana H.C.Watson (Critically Endangered)

Vernacular names

Euphorbia stygiana (Portuguese: Trovisco-macho) is a species of evergreen shrub in the family Euphorbiaceae, endemic to several islands of the Azores. It has a critically endangered subspecies (subsp. santamariae) with only 20 known remaining mature individuals in the wild.

Description

Euphorbia stygiana is an evergreen shrub with low but robust serpentine, green stems; white-veined, thick, leathery blue-dark green leaves and large yellow-green flower heads which are strongly honey-scented in spring and summer (from May to June). It can grow up to about 10 metres (33 ft) tall in its native environment but is often 1.5 metres (4.9 ft) tall and spreads to about 1.5 metres (4.9 ft) wide.[2][3][4]

The leaves are 7–14 by 1.5–3.5 centimetres (2.76 in–5.51 in × 0.59 in–1.38 in) long, slightly pubescent on the bottom side. The fruits are 5–7 millimetres (0.20–0.28 in), striated, subglobous and warty.[5] During cold winters (especially outside its native range) these leaves may turn to a brilliant crimson colour.[6]

It is hardy down to USDA Zone 8b: to −9.4 °C (15.1 °F) and can be propagated through stem cuttings.[4]
Distribution and habitat

Euphorbia stygiana is endemic to all Azorean islands except Graciosa where it inhabits the extremely humid highlands of the archipelago from 300 to 1,100 metres (980 to 3,610 ft) in altitude, especially on Pico Island, in sheltered places such as ravines, craters and dense laurel-Juniperus forests.[5][7][8]
Subspecies
Specimen at the Frankfurt Botanical Garden

There are two known subspecies:

subsp. santamariae – a critically endangered subspecies native only to the island of Santa Maria with less than 20 known mature individuals remaining in the wild, restricted to 343 square kilometres (132 sq mi). The remaining population rests in a steep slope of a valley embedded in a stream, in a humid forest dominated by Pittosporum undulatum.[9] It is a smaller tree, and has a strong apical dominance. Foliage is less leathery with a faint bluish bloom.[3] It also has a less pronounced leaf vein and has fuzzy inflorescences with orange extrafloral nectaries.[10]

subsp. stygiana – the most common subspecies, inhabiting most of the Azorean islands except Graciosa and Santa Maria in high altitude, humid laurel-Juniperus forests.[11]

Threats

The species is mainly threatened by agricultural development, change in land use, and invasive species and the subsequent increase in competition.[12]
Toxicity

Like other members of the Euphorbia genus, E. stygiana has a milky white sap that may cause skin irritation or allergic reaction when in contact with the skin or eye.[4] It is toxic if eaten.[2]
Gallery

References

"Species Details : Euphorbia stygiana H.C.Watson". Catalogue of Life. Retrieved 30 November 2020.
"Euphorbia stygiana". turn-it-tropical.co.uk. Retrieved 1 December 2020.
"Euphorbia stygiana". panglobalplants.com. Retrieved 1 December 2020.
"Euphorbia Species: Euphorbia stygiana". davesgarden.com. Retrieved 1 December 2020.
"Euphorbia stygiana Watson". Natura 2000 Azores. Retrieved 1 December 2020.
"Euphorbia stygiana". rightplants4me.co.uk. Retrieved 1 December 2020.
"Euphorbia stygiana H.C.Watson". Flora-on. Retrieved 1 December 2020.
"Euphorbia stygiana Watson (EUPHORBIACEAE) - Trovisco-macho". siaram.azores.gov.pt. Retrieved 1 December 2020.
"Euphorbia stygiana subsp. santamariae H.Schaef". Flora-on. Retrieved 1 December 2020.
"O trovisco-macho mais raro da Europa". Paulo V. Araújo, Maria P. Carvalho. Retrieved 1 December 2020.
"Euphorbia stygiana". Flora-on. Retrieved September 2, 2020.
"Euphorbia stygiana subsp. santamariae". IUCN. Retrieved 1 December 2020.