Oenothera rosea Aiton (1789:3)

Tavilla, Gianmarco & Lanfranco, Sandro, 2025, Oenothera L. a new genus of alien plant first reported in the Maltese Islands, Phytotaxa 705 (2), pp. 203-211 : 204-208

Oenothera rosea Aiton (1789:3) , in Hort. Kew. [W. Aiton] 2

( Figures 1 and 2 )

≡ Hartmannia gauroides Spach , in Hist. Nat. Vég. 4: 371 (1835), nom. superfl.

≡ Hartmannia rosea G.Don , in Hort. Brit. [Sweet], ed. 3: 236 (1839).

≡ Xylopleurum roseum Raimann , in Nat. Pflanzenfam. 3(7): 214 (1893).

= Gaura epilobia Mociño & Sessé ex Seringe , in A.P.de Candolle, Prodr. 3: 45 (1828).

= Godetia heucki Philippi. in Anales Univ. Chile 84: 473 (1893).

= Hartmannia affinis Spach , in Ann. Sci. Nat., Bot., sér. 2, 4: 167 (1835), nom. superfl.

= Hartmannia virgata Spach , in Nouv. Ann. Mus. Hist. Nat. 4: 361 (1835).

= Hartmannia rosea var. parvifolia Small , in Bull. Torrey Bot. Club 23(5): 181 (1896).

= Oenothera rubra Cavanilles , in Icon. 3: 68 (1796).

= Oenothera purpurea hort. Ex Lamarck, in Encycl. 4(2): 554 (1798), nom. illeg.

= Oenothera virgata Ruiz López & Pavon , in Fl. Peruv. 3: 79 (1802).

= Oenothera psychrophila Ball , in J. Linn. Soc., Bot. 22: 38 (1885).

= Oenothera rosea var. parvifolia J.M.Coulter , in Contr. U.S. Natl. Herb. 1: 38 (1890).

= Oenothera lyrata H.Léveillé , in Monogr. Onothera: 111 (1902).

= Oenothera rosea f. epilobiifolia H. Léveillé , in Monogr. Onothera: 113 (1902).

= Oenothera rosea var. helleri H. Léveillé , in Monogr. Onothera: 111 (1902).

= Oenothera rosea var. lyrata (H. Léveillé) Pitard , in Iles Canaries: 183 (1909).

Perennial (hemicryptophyte) herbs, 10–65 cm tall. Stems ascending to erect, simple or branched, sometimes with longer, spreading hairs, and more densely pubescent in the inflorescence. Leaves alternate, green, with basal leaves oblanceolate to elliptic, 2–5 × (0.5) 1–2 cm, subentire to coarsely dentate, sometimes sinuate-pinnatifid at the base; petioles (0.4) 1–3 cm long; cauline leaves elliptic to oblong-ovate, 1–6 cm long, with margins subentire to sinuatedentate, acute to obtuse apex. Inflorescence in a raceme, flowers erect, hypanthium tube 0.4–0.8 cm long. Sepals 5–8(10) mm long, greenish, frequently coherent and deflexed to one side at anthesis, with short free apices. Petals pink to rose-purple, obovate, 4.5–12 mm long. Stamens with filaments 4–6 mm long, anthers 2.5–4 mm long. Style 8–12(14) mm long, surrounded by anthers during anthesis, ovary usually densely strigillose, 1–1.5 mm long. Fruit a clavate to narrowly obovoid capsule, (4)8–10(12) mm long, 3–4 mm in diameter, with valves angled or weakly winged. Seeds brown, oblong-obovoid to elliptic, 0.6–1 × 0.4–0.5(1) mm, arranged in two or more rows per locule, finely granular-papillate.

Examined specimens:— MALTA. Floriana: Argotti Botanic Garden , 35.892255N, 14.502941E, 22 May 2024, G. Tavilla 58923 ( BI) ; ibidem, San Ġwann: near the roadside, 21 May 2024, S. Lanfranco s.n. (S. Lanfranco herbarium) . ITALY. Tuscany: Pistoia in loc. Serra Mugnai (43.941358 N, 10.968604 E), molte piante in piena fioritura fra il margine N della strada e l’area coltivata della serra, circa 80 m slm, 25 May 2022, G. Ginestri s.n. ( PI061519 ) ; ibidem, Liguria: Sopra Bocca di Magra , al margine della strada per la Punta Bianca , a q. 110m. Ameglia (SP), D. Marchetti s.n. ( PI062818 ) . FRANCE. Gallia, Dept. Basse Pyrénées, Hendaye , ad versuras, 10 August 1954, K.H. Rechinger O- 1185 ( WU0023996 ) . AUSTRIA. Wien, 22 July 2014, B. Knickmann s.n. ( WU0086286 ) . EL SALVADOR. Chalatenango: Depto. Chalatenango, Mpio. San Ignacio, Ctón. Río Chiquito , 2180 m, 89°7’16.16”W, 14°21’39.3”N, 7 May 2019, leg. D. Rodríguez, & P. Galán 7258, det. D. Rodríguez ( B101247496 ) . CHILE. Valparaíso: Región V [Valparaíso]: Prov. Los Andes: Parque Arqueológico Paidahuén , 32°49’1’’S, 70°34’39’’W, 869 m, 1 November 2015, M.F. Gardner & S.G. Knees 9319 ( E00719052 ) . PORTUGAL. Lisbon: Lisboa (Lusitanica, Estremadura), Belém , Praça do Império , 5 m, in hortis, 30 May 1972, M. Martins 311 ( P04886041 ) ; ibidem, Coimbra: Choupal , A. Moller s.n. ( P04891217 ) . MEXICO. MPIO Ixtapaluca, SE of Chapingo : Canada xaltomatla, at bend of road at canyon bottom, 2600 msm, Sierra Nevada , 13 August 1984, D. Randolph 308 ( MT00194233 ) .

Distribution and ecology:— Oenothera rosea is widely naturalized worldwide in tropical and subtropical areas. The native range of this species extends from Southern California to Southern Texas, as well as Western and Southern South America, Cuba, and Jamaica ( POWO 2024). The species is considered alien in the Euro-Mediterranean region and is currently found in several locations, including Portugal, Spain, the Azores, the Canary Islands, the Balearic Islands, the Cape Verde archipelago, Madeira, Italy, Sicily, Sardinia, Belgium, France, the UK, Israel, Sweden, and Algeria ( Nicotra 1904, Hamel 2016, Raab-Straube 2018 +, Gonçalves Silva & Ferreira 2019, Danin & Fragman-Sapir 2004, POWO 2024). It should be noted that the earliest historical record of O. rosea in Sicily (the closest island to Malta) was documented by Nicotra (1904) in the Messina territory, where it was sporadically found in several locations. Currently, there is no proven record of the genus Oenothera or O. rosea in the literature regarding the Maltese Islands. Casha (2020), in his floristic list for the Maltese territory, mentions Oenothera lindheimeri (Engelmann & A.Gray 1845:217) W.L. Wagner & Hoch (2007:213) as well as O. rosea . However, these records lack scientific support, as they are based on generic locations and personal communications rather than verified observations. Additionally, the only available photograph of O. lindheimeri noted by the author was taken in a public garden of cultivated plants. Therefore, there is no evidence or herbarium samples to confirm the presence of these plants. In light of this, we document the first confirmed report of O. rosea in the Maltese Islands, found in two different locations: near the San Ġwann area and within the Argotti Botanic Gardens in Floriana ( Figure 3 ). It is important to note that one population of O. rosea is situated in close proximity to the Wied Għollieqa Nature Reserve. From an ecological viewpoint, O. rosea grows within plant communities of perennial species that typically represent the early stages of ecological succession on substrates influenced by human activity. These communities thrive in arid, nutrient-poor soils, often characterized by substantial amounts of gravel or fragmented debris. In Malta, O. rosea has been observed growing alongside Diplotaxis tenuifolia ( Linnaeus 1755:18) Candolle (1821:632) , Verbena officinalis Linnaeus (1753:20) , Lysimachia arvensis ( Linnaeus 1753:148) U. Manns & Anderberg (2009:51) , and Oxalis pes-caprae Linnaeus (1753:434) in both urban and rural disturbed areas.

Phenology:— Specimens in flowers were collected and observed in May. Flowering and fruiting time from April to July.

Discussion:— In Malta, two stands of Oenothera rosea have been discovered, located approximately 2.5 km apart along a straight line. The genus Oenothera is native to North and South America, however, several species have been introduced and subsequently naturalized worldwide, including in Europe ( Mihulka & PysÏek 2001, Márquez-Flores et al. 2018). Notably, around 90 taxa of Oenothera are reported in Europe ( Raab-Straube 2018 +), highlighting the widespread distribution of this genus within the Mediterranean region. Although O. rosea is currently restricted to anthropogenic environments in Malta, the potential for its invasion of natural habitats cannot be excluded. Indeed, in South Africa, O. rosea has invaded grasslands, mountainous areas, and coastal vegetation ( Frean et al. 1997). The most invasive Oenothera species tend to exhibit high germination rates and prolific seed production. The biology of O. rosea suggests a significant potential for invasiveness. The species’ notable reproductive capacity and adaptability, particularly its propensity to quickly establish enduring seed banks ( Meiyu et al. 2009). The species shows rapid establishment as the dominant species, underscoring its invasive potential and ecological impact. These traits endow O. rosea with a considerable capacity for colonization and expansion into surrounding areas, for example within the Wied Għollieqa Nature Reserve in Malta. Consequently, this non-native species is identified as an additional threat to the indigenous Maltese flora. Considering the central Mediterranean location of the Maltese archipelago, the recent and increasing records of Oenothera species in Sicily warrant careful attention regarding the potential for this island to serve as a secondary diffusion hub toward Malta. Recent floristic studies in Italy and Sicily, have highlighted an ongoing expansion of Oenothera . The numerous new reports from various Sicilian localities (e.g., Messina, Agrigento, Lipari, and Panarea) suggest either multiple introduction events or, importantly, the successful establishment and subsequent intra-regional dispersal of Oenothera species ( Crisafulli et al. 2013, Stinca et al. 2017, Barone et al. 2023, Cambria et al. 2023, Galasso et al. 2024). These species are often found in ruderal habitats, alongside roadsides, and in disturbed areas, which are plentiful and can function as corridors for spread. Given the geographical proximity of the Maltese Archipelago to Sicily, coupled with shared Mediterranean climatic conditions, Malta is especially vulnerable to the arrival and potential establishment of Oenothera species currently spreading in Sicily. Therefore, the documented proliferation of Oenothera in Sicily serves as a crucial bioindicator of potential future invasions for Malta. The capacity of this genus to naturalize and, in some cases, become invasive, highlights the ecological risk associated with its uncontrolled spread into new insular environments like Malta. Malta has over 450 alien taxa, whereas Sicily accommodates more than 600 ( Mifsud et al. 2022). Considering their respective land areas, 316 km ² for Malta and 25,711 km ² for Sicily, the density of alien taxa in Malta is approximately 1.42 taxa per km², in contrast to 0.023 taxa per km ² in Sicily. This indicates that the density of alien taxa in Malta is roughly 61 times greater than in Sicily. The pathways through which Oenothera rosea was introduced to Malta are likely diverse, and several hypotheses can be proposed. Indeed, Oenothera rosea has been introduced to various parts of the world, including Europe, both intentionally, as an ornamental garden plant, and accidentally, through ballast soil, maize seeds, or other transported goods ( Rostański 1991). Furthermore, the possibility of introduction via birds cannot be ruled out, as Malta serves as a stopover site for numerous migratory bird species.

Additional specimens examined:— GREECE. Thessaly: Oenothera speciosa Nutt. , Griechenland , Nomos Magnisia , Nördliche Sporaden , Skiátos , NW- Küste , Megalos Aselinos Bay , fast ausgetrocknetes Bachbett , 5 m, 39°10’17”N, 23°25’21”E, K. Rainer s.n. ( GJO0125678 ). USA. Florida: Oenothera speciosa Nutt., Jacksonville , in waste place, 12 May 1930, leg. F.S. Blanton 6271, det. P. Raven ( P05182487 ). MEXICO. Coahuila: Oenothera speciosa Nutt. , Rio Grande valley near Diaz , 700 ft., 23 April 1900, C.G. Pringle s.n. ( P04889292 ) .

Key for the identification of Onagraceae family and Oenothera rosea in the Maltese Islands

1. Sepals and petals 2; fruit 1–4 mm, indehiscent, bristly, covered with hooked hairs, 1 or 2 seeded........................................ Circaea

- Sepals 4 or 5; petals 4, 5 or apetalous; fruit dehiscent or a berry, without hooked hairs ...................................................................2

2. Herbs; sepals 4 or 5; petals 4, 5 or apetalous; stamens 4 or 10; fruit 2–5 mm, sepals persistent on the fruit ....................... Ludwigia

- Shrubs; fruit a berry................................................................................................................................................................. Fuchsia

- Herbs; sepals and petals 4, conspicuous; stamens 8; fruit more than 5 mm, sepals no persistent on the fruit...................................3

3. Petals purplish-pink to withe, never yellow; hypanthium up to 2.5(5) mm; seeds with a chalazal tuft of hairs (pappus)................... ............................................................................................................................................................................................. Epilobium

- Petals yellow, rarely pink; hypanthium 1–11(13) cm; seeds without pappus................................................................4 ( Oenothera )

4. Petals yellow, sometimes with a red spot at the base; cylindrical capsules or tapering towards the apex ........................................... .................................................................................................................................................................. Oenothera sect. Oenothera

- Petals withe or purplish-pink..............................................................................................................................................................5

5. Petals withe, 2.5–4 cm; hypanthium 1–2 cm; fruit club–shaped to obovoid, 1–1.8 cm long .............................................................. .............................................................................................................................................. Oenothera speciosa (sect. Hartmannia )

- Petals pink to rose purple, 0.5–1.2 cm; hypanthium 0.4–0.8 cm; fruit club–shaped, 1.3–3 cm long .................................................. ................................................................................................................................................... Oenothera rosea (sect. Hartmannia )

Figures

FIGURE 1. Oenothera rosea. A. Habitus of the plant in its location of occurrence. B. Detail of the flower. C. O. rosea plants in San Ġwann (Malta). D. O. rosea plant in Floriana (Malta). (Photos by G. Tavilla).

FIGURE 2. Herbaium specimen of Oenothera rosea kept in BI.

FIGURE 3. Geographical distribution of Oenothera rosea (red dots) in Malta. Base map (modified): Google Maps (©2024 Google, Imagery ©2024 TerraMetrics, Map data ©2024 Google).