First report of a well-established Ambrosia ( Asteraceae ) to the non-native African flora

El Mokni A-A., El Mokni Ra. & El Mokni Ri.: First report of a well-established Ambrosia ( Asteraceae ) to the non-native African flora. — Fl. Medit. 33: 243-250. 2023. — ISSN: 1120-4052 printed, 2240-4538 online. Ambrosia confertiflora a perennial herb native to North America and Caribbean has been recorded as a new alien to the vascular flora of African continent, second report to the Mediterranean area. In Tunisia, A. confertiflora is reported naturalized from few localities in the centre of the country where the species has established small and extended populations in surrounding ruderal disturbed habitats. A short morphological description as well as its distribution and habitat in Tunisia with color photos are presented. Moreover, a key to the Ambrosia species in the African continent is here firstly provided.


Introduction
Since few decades a tendency for invasion of foreign plant species into the southern Mediterranean flora becomes ever more prominent (see e.g.Véla & al. 2013; Meddour & El Mokni 2016; Sukhorukov & al. 2018, 2019; El Mokni & Iamonico 2019; El Mokni & Verloove 2019; El Mokni & Domina 2020; El Mokni & al. 2020; Verloove & al. 2020) where the Asteraceae remains one of the largest families of flowering plants and contains major globally naturalized flora (see e.g.El Mokni & El Aouni 2011; Hamel & Azzouz 2018; El Mokni & Iamonico 2018a, 2018b; El Mokni & Domina 2018a, 2018b; El Mokni & Véla 2018; Miara & al. 2018; Verloove & al. 2020; Sakhraoui 2021; El Mokni & al. 2022).Ambrosiinae Less is a subtribe of the Heliantheae Cassini tribe (Asterales, Asteraceae), including almost eight genera among which Ambrosia L. and Xanthium L. are widely spreading in Africa.The genus Ambrosia counts more than 50 species, with ragweed or bursage as the commonly known member.Ambrosia is naturally occurring in the new world, mainly in North America (Leon de la Luz & Rebman 2019; WFO 2023).It is distributed mostly in the southwestern United States and the nearby North Mexico with an apparent centre of origin and diversity in the Sonoran Desert, but a few species can be found in Central America and South America (Payne 1966).In Africa, the genus includes almost five casual to naturalized species (APD 2023).
During field work at the centre of Tunisia (N-Africa), an extended population of one Ambrosia that looks new to the African continent, has been found.Details about the identity of this new established Ambrosia in continental Africa and its habitats are presented.Moreover, a key to the Ambrosia species in Africa is here proposed.

Material and methods
Several botanical expeditions were carried through different regions of centre of Tunisia since 2015 to make updates about its wild/non-native flora, especially the undocumented ones.Data on the plant populations and the habitats of the recoded taxa were also collected.For the identification of the species, relevant literature (see e.g.Keil 2012; Flora of North America 2017; EPPO 2019) and examination of specimens preserved at some accessible herbaria were used (MPU, NYBG and P, acronyms follow Thiers 2023 [continuously update]).Collected specimens are deposited at the personal herbarium of the author (Herb.R. El Mokni) housed in the Herbarium of Monastir University (not listed in Index Herbariorum).

Results
As stated in the introduction, the unknown species proved to be Ambrosia confertiflora DC., a species with native range restricted to the North America (mainly Mexico, Villaseñor Ríos 2016) and Caribbean (Puerto Rico, EPPO 2019 :50), not known yet in the African continent and second report for the Mediterranean area (CABI 2023).All discovered population and subpopulations from different sites of centre Tunisia seem to be well established, suggesting that the species is naturalized and could be more widespread within surroundings if not in other parts of Tunisia and N-Africa.The given morphological description is based in part from material collected in this study.Ambrosia confertiflora DC., Prodromus Systematis Naturalis Regni Vegetabilis 5: 526.
Phenology in Tunisia -Flowering and fruiting times October to December (sometimes up to January).
Geographical distribution and rate of invasiveness (Fig. 2) -Native to northern Mexico and south-western USA, Ambrosia confertiflora has been reported as introduced and naturalized in Australia (New South Wales, South Australia and Queensland) by Watt (1987) and Council of Heads of Australasian Herbaria (2019) and also Palestinian occupied territory including the West Bank (Yair & al. 2017) where it can form very dense stands and outcompetes other plants.Among several other Ambrosia species that have proved to be invasive after being introduced to areas outside of their native ranges (A.artemisiifolia L., A. psilostachya DC., and A. trifida L.), A. confertiflora spreads very fast, reproducing from seeds and through vegetative propagation, and is considered to have the fastest rate of spread among land invasive alien plants in the Palestinian occupied territory where low winter temperatures in the Mediterranean basin do not seem to affect survival.The numerous spiny burrs stick to the fur of mammals but also spread in flowing water, particularly during floods (EPPO 2019).
Distribution and habitat in Tunisia -Ambrosia confertiflora grows mainly in moist localities along the roadsides, in waste places and edges of cultivated fields, more rarely in human-made habitats on loamy and sandy substrates within ruderal vegetation (mainly Opuntia ficus-indica (L.) Mill.) and abandoned rocky soils from 85 to 165 m a.s.l.At the sites where it was discovered (Limaya, Menzel chaker, Sfax, CE of Tunisia), it continued growing through winter, spring, and summer but flowering occurred only from October and no benefits were attributed to the plant for the Limaya's habitants.

Diagnostic key to species of Ambrosia in Africa
The key below, based on published literature (see e.g.Strother 2006; Karrer & al. 2021; Jepson Flora Project 2023), can be used to distinguish the six species of Ambrosia known from the African continent, so far: 1a.Taproots…….

Discussion
Ambrosia confertiflora is one more reported taxon for the non-native flora of Africa, second report to the alien Asteraceae for the Mediterranean area.Two major established populations/subpopulations were here firstly found in centre Tunisia.The plant produces a large amount of pollen (as with the other Ambrosia species) which is considered to be severely allergenic (Yair 2017), causing hay fever and contact dermatitis in susceptible people and classified as noxious (Parsons & Cuthbertson 2001).In the nearer future, all sites of the new alien plant have to be under continuous monitoring to limit its spreading at least via disper-Flora Mediterranea 33 -2023 sal seeds by traffic over very long distances and storm water run-off might along roadsides over short or mid-distances and as a second urgent step and due to its almost not very extended populations, actions for manual eradication (pulling out) must be taken before the flowering period.We strongly discourage the application of herbicides as some of these chemical products have the capacity to move in the environment away from the target area, and to cause damage to non-target plants and animals, besides the ability to cause a loss of vegetation cover and, consequently, an increase in erosion problems.

Fig. 1 .
Fig. 1.Ambrosia confertiflora in Tunisia : a) habit of the plant and ruderal habitat within roadsides; b) detail of the inflorescence.Photographs by R. El Mokni.a b

Fig. 2 .
Fig. 2. Actual worldwide distribution area of Ambrosia confertiflora red color for CABI summary data and purple color (Tunisia, African continent) for the present work.