Aloe arborescens Miller (1768

Smith, Gideon F., Figueiredo, Estrela, Verloove, Filip, Klopper, Ronell R. & Silva, Vasco, 2023, An annotated catalogue of Aloe and Aloiampelos (Asphodelaceae subfam. Alooideae) naturalised and escaped in continental Portugal, Phytotaxa 629 (1), pp. 35-52 : 36-38

1. Aloe arborescens Miller (1768 : first page headed “ALO-ALO”, species # 3) ( Fig. 1A–F ).

Locally used synonyms:—None recorded.

Common name(s):— Portuguese: aloé, aloé-candelabro, babosa, foguetes-de-natal, vela ( Güemes 2013: 312). English: candelabra aloe, krantz aloe ( Grace et al. 2011).

Description:—Shrub, 1.5–3.5 m tall, much-branched. Stems erect to slanted sideways, upper parts clothed in persistent dried leaves. Leaves densely rosulate at branch apices, spreading-recurved, 40–60 cm long, 4–7 cm wide at base, lanceolate-attenuate, dull green to grey-green, distinctly tinged reddish in dry conditions, lacking whitish maculations, texture smooth; margin whitish, not horny; marginal teeth 5–20 mm apart at mid-leaf, 3–5 mm long, firm, pale; exudate pale yellow. Inflorescence 0.6–1.0 m long, erect, usually simple, occasionally with 1 or 2 short branches. Raceme 20–35 cm long, conical to conical-cylindric, dense-flowered. Floral bracts 15–20 × 10–12 mm. Pedicels 30–40 mm long. Flowers: perianth 30–40 mm long, 7 mm across ovary, of ± even diameter throughout, very slightly narrowed above ovary, widening to middle, narrowing slightly towards mouth, apices flared, cylindric-trigonous, bright orange to scarlet, dark green-tipped in bud, often turning pinkish at anthesis; outer segments free to base; stamens and style exserted to 6 mm. Capsule ± 2 cm long, oblong.

Flowering time:—(November–)December–January(–February).

Habitat:—Mostly on coastal rocky slopes ( Franco & Afonso 1994: 46).

First mention of the species as naturalised in Portugal:—1980 ( Webb 1980: 21).

Localities recorded:— Franco & Afonso (1994: 46) recorded it for “CW. olissip., CS.arrab.”, and Pedro (1991: 105) recorded it for Arrábida, i.e., in the centre, in the Lisbon area. Güemes (2013: 312) recorded it for E and Ag. Presently the distribution is extended to: DL, BL (for example at Nazaré), E (for example at Cascais, Oeiras, Lisbon, and Arrábida), BAl (for example at Praia da Ilha do Pessegueiro and Porto Covo), and Ag.

Country / region of origin:—Southern Africa, from the Cape Peninsula (where it has arguably become naturalised), along the south and east coast of South Africa, somewhat inland through the provinces of Western Cape, Eastern Cape, and KwaZulu-Natal, and in the interior of Mpumalanga and Limpopo, just entering the eastern Free State, as well as further north, in south-tropical Africa, to Mozambique and the eastern mountains of Zimbabwe and Malawi ( Smith et al. 2008, 2012a).

Secondary distribution range:— Aloe arborescens is sparingly naturalised worldwide in areas with a Mediterranean climate. It is reportedly known from the western Mediterranean area: France (Rivièra and Corsica; Tison & de Foucault 2014), Spain (for example Guillot Ortiz et al. 2008, Aymerich & Sáez 2019), Gibraltar ( Lamb 1996), Italy (naturalised only in Sardegna, casual elsewhere; Galasso et al. 2018, Pavone et al. 2022), and Malta ( Mifsud 2022). It is furthermore naturalised in the Canary Islands ( Dobignard & Chatelain 2010; elsewhere in northern Africa, it is probably merely cultivated or ephemeral). It is also naturalised on the eastern coast of Australia (New South Wales, Queensland, and Victoria; Randall 2007, Weeds of Australia 2023), New Zealand ( Schönberger et al. 2021), California in the U.S.A., Japan, South Korea, and the Marshall Islands. In some areas of its secondary range, A. arborescens is considered to be a minor environmental weed.

The origin of most of the A. arborescens plants now grown in the northern hemisphere, is likely from plants cultivated at the Cape of Good Hope (now in the Western Cape Province of South Africa) in the 17 th and 18 th centuries. Using leaf exudate chemistry, Reynolds & Herring (1991) proved that the origin of A. arborescens growing in Gibraltar is indeed from the Western Cape, South Africa, and not from further north in the natural distribution range of the species.

Status in Portugal:—Naturalised.

References:— Webb (1980), Franco & Afonso (1994), Almeida & Freitas (2006), Smith & Figueiredo (2009), Almeida (2012), Güemes (2013), Silva et al. (2015).

Notes:— Aloe arborescens is a distinctive, large-growing species of up to 5 m tall. It grows as a much-branched shrub with rather robust stems and branches, as opposed to Aloiampelos ciliaris that has thin, slender, and weak branches. The greyish green leaves are carried in dense rosettes, with the leaves sporting pale yellow teeth on the margins. Stems and branches are usually clothed in the dried remains of desiccated leaves. The inflorescences— elongated, conical racemes—are usually simple and dense-flowered ( Smith et al. 2008 c, 2012a, Klopper et al. 2020: 21).

It is not known whether A. arborescens introduced to Portugal was definitely from South Africa, where it occurs virtually along the entire southern and eastern coasts, from the Cape Peninsula eastwards, and would have been easily detected by passing ships that made landfall, for example at Plettenberg Bay ( Figueiredo & Smith 2017: 31), or instead sourced from Mozambique, a former Portuguese colony, where it is also indigenous, or from both countries. Similar uncertainty surrounded the original location from which A. spicata Linnaeus filius (1782: 205) was collected and taken to Portugal ( Glen & Hardy 1995, 2000: 118–119).

Regardless of the origin of material of A. arborescens that is grown in Portugal, the species is very commonly cultivated in the country, from the Algarve in the south to at least as far north as Porto ( Fig. 1A–C ).

Aloe arborescens was recently recorded from Nazaré ( Smith & Figueiredo 2009) ( Fig. 1D ). The species is here recorded for the first time from Praia da Ilha Pessegueiro ( Fig. 1E ) and from Porto Covo ( Fig. 1F ), two locations along the Alentejo coast.

Mateus et al. (2015) recorded a species of thrips, Hercinothrips dimidiatus Hood (1937: 105) ( Thysanoptera : Thripidae ), on A. arborescens from several localities in the vicinity of Lisbon. This was the first record of this thrips species for Europe, and Mateus et al. (2015) speculate that its introduction into Portugal resulted from infected plants from South Africa having entered Portugal via Lisbon, a major port city. Hercinothrips dimidiatus was first described from South Africa. Material of A. arborescens from well beyond Lisbon, for example from Coimbra, appears to also have been infected with the thrips (personal observations by GFS and EF).

Figures

FIGURE 1. Aloe arborescens in Portugal. A. Cultivated in beds next to the Estufa Fria, Lisbon. Photograph taken on 30 December 2013. B. Cultivated near the old town centre of Coimbra, en route to the University of Coimbra. Photograph taken on 8 January 2018. C. Cultivated in the Botanical Garden of the University of Porto. Photograph taken on 22 December 2017 (see Smith & Figueiredo 2014). D. Escaped into natural vegetation at Nazaré, Estremadura (see Smith & Figueiredo 2009). Photograph taken on 4 October 2008. E. Naturalised at Praia da Ilha Pessegueiro, along the Alentejo Litoral coast, near Porto Covo. Photograph taken on 30 December 2017. F. Naturalised at Porto Covo. Photograph taken on 30 December 2017.All photographs by Gideon F. Smith.