Introduction
The exceptional floristic richness and high level of endemism in North Africa are well documented, largely due to its geographic position within the southern shore of the Mediterranean biodiversity hotspot (Médail and Quézel 1997, Véla and Benhouhou 2007). In Algeria, this diversity also extends to sub-Mediterranean biogeographical sectors such as the Western Saharan Atlas and adjacent regions (Gordo and Hadjadj-Aoul 2019, Gordo 2021). However, this botanical heritage is increasingly threatened by multiple factors such as recurrent drought (Bouarfa et al. 2022) and the rising presence of alien plants species in the Naâma region (Gordo and Uotila 2024, Gordo et al. 2025).
The latter work documented 51 exotic plant species, most of them originating from the Americas. Based on their degree of naturalisation, 18 taxa were classified as naturalised. These species require monitoring to anticipate the arrival of future invasive or potentially invasive species, and to assess their impact on endemic flora and fragile ecosystems such as steppes and wetlands. For this purpose, tools such as the Extended Environmental Impact Classification for Alien Taxa (EEICAT) recently proposed by Carneiro et al. (2026) are particularly relevant.
Within this context, species of the genus Helianthus L., native to the Americas and already known as casual aliens in Algeria, have now been recorded for the first time in the Naâma region. Until now, only H. annuus L. (sunflower) had been reported as a casual alien in North Africa (see e.g., El Mokni et al. 2022) and more recently in Algeria (Rebbas 2022, Sakhraoui et al. 2024, Sarri et al. 2024, Taieb Brahim et al. 2024).
The present contribution documents the first record of H. debilis Nutt. subsp. cucumerifolius (Torr. & A.Gray) Heiser in North Africa and provides notes on its potential naturalisation in Algeria.
Material and methods
Field surveys conducted by the first author since 2022 have focused on the flora of urban, peri-urban, and agricultural ecosystems throughout the Naâma region (Naâma Province, West of Algeria). These surveys covered a wide range of habitats, from relatively undisturbed environments such as green spaces, farms, and vegetable gardens to highly disturbed habitats including roadsides and ruderal areas.
In the latter habitats within the city of Aïn Sefra (southern Naâma Province; Fig. 1A), about thirty individuals of a branched sunflower were observed in three stations that were initially misidentified as H. annuus. Photographs were taken in the field and several samples were collected, deposited later in the Herbarium of the University of Naâma (UN, Algeria). Some duplicates were sent to the Herbarium of Meise Botanic Garden (BR, Belgium). In BR, voucher specimens were compared with material of the H. debilis complex and with H. petiolaris Nutt. After detailed examination, the identification was refined to the subspecific level as H. debilis subsp. cucumerifolius. Nomenclature follows the International Plant Names Index (IPNI 2026). The morphological description was based primarily on the studies of Heiser (1956), Schilling (2006) and Tseng et al. (2008).
Fig. 1. Helianthus debilis subsp. cucumerifolius (Torr. & A.Gray) Heiser. A – Location of Aïn Sefra (Naâma Province, Algeria), B – habitat, C – habit, D – phyllaries, E – leaves, F – disc palea (photos: B. Gordo)
Results and discussion
Helianthus debilis Nutt. subsp. cucumerifolius (Torr. & A.Gray) Heiser (synonyms H. cucumerifolius Torr. & A.Gray, H. debilis Nutt. subsp. cucumerifolius (Torr. & A.Gray) Heiser var. cucumerifolius (Torr. & A.Gray) A.Gray), H. debilis Nutt. var. cucumerifolius (Torr. & A.Gray) A.Gray, H. debilis f. cucumerifolius (Torr. & A.Gray) Voss).
An annual (or perennial) plant, branched from the base, 40–150 cm tall. Stem erect, hispid, sometimes purplish spotted. Leaves numerous, alternate, toothed, and slightly undulate; blades oval-triangular to oval-lanceolate, with a cordate or truncate base, occasionally cuneate. Petiole 2–9 cm long; blade 5–10 × 2–7 cm. Peduncles 15–50 cm long. Capitula with 10–20 yellow ray florets and more than 25 tubular disc florets, 2–5 cm in diameter. Involucre 1.5–2.0 cm in diameter; phyllaries 16–30, lanceolate, long-acuminate, 1–2.5 cm long, and 0.3–0.5 cm wide. Cypselae 7–13 mm long (Fig. 1B-F).
Material examined: Algeria: Naâma, Ain Sefra, Hydra city, 32°44'28.54ʺ N, 0°35'6.42ʺ W, 1150 m a.s.l., rubble on sandy soils, 25 March 2025, B. Gordo s.n (UN). Naâma, Ain Sefra, near the old train station, 32°45'19.41ʺ N, 0°34'57. 46ʺ W, 1080 m a.s.l., 18 September 2023, B. Gordo s.n. (BR).
It should be noted that plants of H. petiolaris (prairie sunflower) closely resemble the plants observed in Aïn Sefra, as several morphological characteristics are shared between both taxa. The main diagnostic difference in H. petiolaris lies in the presence of a tuft of long, white bristles surmounting some of the central paleae (Tab. 1). In addition, H. petiolaris usually behaves as a messicolous weed, whereas H. debilis subsp. cucumerifolius is most commonly used as an ornamental species (Heiser 1955, Seiler and Rieseberg 1997).
Tab. 1. Diagnostic characteristics distinguishing Helianthus debilis subsp. cucumerifolius, H. annuus, and H. petiolaris. Data mainly based on Schilling (2006) in Flora of North America and field observations from Algeria.
Helianthus debilis subsp. cucumerifolius may also be confused with H. annuus, a species widely cultivated and occasionally escaping locally in Algeria. However, several morphological characteristics allow both taxa to be distinguished. H. debilis subsp. cucumerifolius is generally a smaller and more slender plant, often 40–150 cm tall, whereas H. annuus typically reaches 1–3 m. The capitula of H. debilis are usually smaller (2–5 cm in diameter) and often born on long peduncles, frequently with several heads per plant, while H. annuus usually produces larger capitula, often solitary, and markedly larger (Tab. 1). In addition, the leaves of H. debilis are typically smaller, thinner, and more triangular-ovate, whereas those of H. annuus are broader and more robust. In the field, H. debilis can therefore be recognised by its smaller stature, branching habit, and relatively small flower heads compared with the robust and often single-headed H. annuus. Misidentifications are likely when small or poorly developed individuals of H. annuus occur in disturbed habitats.
Helianthus debilis subsp. cucumerifolius is native to North America, where its natural distribution extends from southwestern Georgia, south to central peninsular Florida, and west to central Texas (Schilling 2006). Outside its native range, the taxon has been reported in numerous regions, including Austria, the Azores, Bangladesh, China, Cuba, Czechia, Slovakia, France, Germany, India, Japan, Java, Korea, KwaZulu-Natal, Malesia, Mozambique, the Northern Provinces of South Africa, Norway, Queensland, Taiwan, and Western Australia (POWO 2026, WFO 2026).
Helianthus debilis subsp. cucumerifoluis is an annual (or perennial) species that typically flowers from spring to autumn. Its life cycle ends with the onset of the first frosts, which in the study area generally occur in December. The species was recorded in ruderal habitats together with typical disturbance-tolerant plants such as Chenopodiastrum murale (L.) S.Fuentes, Uotila & Borsch, Chenopodium album L., Senecio glaucus L. subsp. coronopifolius (Maire) C.Alexander and Sonchus oleraceus L. It also occurs in sandy habitats with psammophilous species including Bassia muricata (L.) Asch., Eremobium aegyptiacum (Spreng.) Asch. ex Boiss. subsp. longisiliquum (Coss.) Maire and Erucaria pinnata (Viv.) Täckh. & Boulos.
In Aïn Sefra, the populations were found in open and highly disturbed habitats such as rubble and waste ground, usually on sandy substrates with a sand content exceeding 80 % (Fig. 1). The city experiences an arid bioclimatic regime with annual precipitation generally below 200 mm. Geographically, Aïn Sefra lies at the southern margin of the Mediterranean region, forming an ecological transition zone between the Mediterranean biome and the Sahara (Gordo 2021).
Based on our field observations, the taxon appears to be in the process of naturalisation, as it was recorded at several sites within the city of Aïn Sefra. Continued monitoring is therefore required to assess the future dynamics of these populations in their new environment.
Additional botanical surveys across Algeria would also be valuable, particularly in the sites where populations have previously been identified as H. annuus. Indeed, the subpopulation illustrated by Sarri et al. (2024) may correspond to H. debilis subsp. cucumerifolius. Likewise, recent reports of H. annuus in northern Algeria (Taieb Brahim et al. 2024) could potentially refer to this taxon and deserve re-examination.
Author contribution statement
B.G. – field surveys, specimen collection, preliminary identification and manuscript preparation; F.V. – taxonomic identification, verification of specimens and critical revision of the manuscript.
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