The vegetation will evolve as you continue down to the south.
A particularly rich flora will accompany your steps, from the famous tea of the Aubrac (Calamintha grandiflora) and the dog tooth (Erythronium dens-canis) to the Salzmann pines of Saint-Guilhem-le-Désert. There are many orchids in the spring including some native varieties (Ophrys d’Aymonin). Carlina (Carlina acanthifolia) and angel hair (Stipa pennata) share the space on the causses. Not to forget the superb pulsatilla (Pulsatilla vulgaris var. Costeana) and the adonis of spring (Adonis vernalis).
On the Aigoual the great gentian (Gentiana lutea) and the martagon lily (Lilium martagon), Saint Anthony’s laurel (Epilobium angustifolium), the Eupatorium cannabifolium and the cévennes thale cress (Arabis cebennensis) are native. Further south the boxwood (Buxus sempervirens) tends to enclose the dry meadows, which are sheep or cattle paths. The saskatoon (Amelanchier ovalis) perfumes the spring by opening its white flowers; asphodels (Asphodelus cerasiferus) thrive where other species would not.
The most common trees are : sylvestre pine (Pinus sylvestris), beech (Fagus sylvatica), spruce (Picea abies), cedar (Cedrus atlantica) ; a few species of oaks : evergreen, pubescent, sessile and common oaks. On the heights a few larches (Larix decidua) and hooked pines (Pinus uncinata). Plantations here and there of Austrian black pines (Pinus nigra subsp. Nigra) in high growing forests.
Not to forget, in this inventory (far from being exhaustive), the chestnut tree, more a Cevenol tree and formerly grown in orchards, now abandoned, which fed whole generations with its fruits.
Basic advice :
Rather take good photos than pick plants. Many species are under departmental or national protection and gathering plants is forbidden in the national park.