Campanulaceae (incl. Lobeliaceae)
Two representatives of Legousia (L. hybrida (L.) Delarbre and L. speculum-veneris (L.) Chaix) are usually claimed as natives in Belgium (Lambinon & al. 2004) but they evidentally are at most archaeophytes. At present both are still sometimes seen in port areas as (ephemeral) grain aliens but they are nearly extinct as weeds of arable land in Belgium. Some plants of the latter are aberrant in having relatively shorter, densely hirsute-ciliate calyx teeth, a character often encountered in L. pentagonia (L.) Thell. However, in other respects these plants do not differ from L. speculum-veneris (corolla and capsule length, etc.). These species are known to intergrade in areas where they grow together. The plants seen in Belgium possibly represent such hybrids rather than genuine L. pentagonia (see also Wahlsteen & Tyler 2019).
In addition to native Wahlenbergia hederacea (L.) Reichenb., a second species of this genus has occurred as an ephemeral wool alien in the valley of river Vesdre. The corresponding collection being insufficient it has not been possible so far to identify this plant properly.
1. Flowers slightly to distinctly zygomorphic (bilaterally symmetric). Filaments connate at base (to form a distinct tube around style). Style bilobed at apex === 2
1. Flowers actinomorphic (radially symmetric). Filaments free. Style branches 2-3(-5) === 3
2. Leaves irregularly pinnatifid. Corolla not split === Isotoma
2. Leaves entire, with minutely toothed margins. Corolla split to base on upper side === Lobelia (incl. Pratia)
3. Inflorescence subtended by an involucre of bracts, always densely capitate to spicate. Corolla lobed almost to base, lobes linear to lanceolate (native) === Jasione and Phyteuma
3. Inflorescence without an involucre. Corolla not lobed to base with wider lobes === 4
4. Style much longer than the corolla. Corolla tube cylindrical, much longer than wide (less than 2 mm across) === Trachelium
4. Style not or hardly exceeding corolla. Corolla tube at least 3 mm wide, not cylindrical and much longer than wide === 5
5. Fruit (and ovary) angular and cylindrical, more than 3x as long as wide. Always annual (native) === Legousia
5. Fruit (and ovary) more or less terete, ovoid-globose, ca. 2x as long as wide. Usually biennial or perennial, rarely annual === 6
6. Stem filiform, slender and procumbent. Capsule opening by valves. Flowers always solitary, axillary (native) === Wahlenbergia
6. Stem usually more robust, erect or decumbent to ascending. Capsule opening by pores. Flowers usually in multi-flowered racemes, panicles or congested heads === Campanula
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Wahlsteen E. & Tyler T. (2019) Morphometric analyses and species delimitation in Legousia (Campanulaceae). Willdenowia 49: 21-33. [available online at: https://bioone.org/journals/willdenowia/volume-49/issue-1]