Cistaceae
The Cistaceae family accommodates, in its current circumscription (i.e., with Halimium (Dun.) Spach included in Cistus L.), eight genera, two of which native in Belgium: Fumana (Dun.) Spach and Helianthemum Mill. (Lambinon & Verloove 2012). Numerous species from these and several other genera are cultivated as ornamentals (e.g. Cullen & al. 1997, Jäger & al. 2008). Out of these, at least one has been recorded as an escape from cultivation in Belgium. In addition, native Helianthemum nummularium (L.) Mill. (and perhaps also H. apenninum (L.) Mill.) are sometimes seen as escapes or garden throw-outs, also in areas where they are not originally native.
1 Leaves linear, alternate. Outer stamens sterile (native) === Fumana
Leaves wider, opposite. All stamens fertile === 2
2 Sepals 3. Stipules absent === Cistus
Sepals 5. Leaves with distinct stipules (native) === Helianthemum
Literature:
Cullen J. & al. (eds.) (1997) The European Garden Flora, vol. 5. Cambridge University Press, Cambridge.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Lambinon J. & Verloove F. (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.