The small spaces between rocks, and stone pathways are tough area to grow anything except weeds, but here are a few plants that thrive between the cracks and crevices.

Creeping Thyme  (Thymus serpyllum):  Excellent for pathways,  grows flat and tolerates foot traffic.  Likes well-drained soil.  Soft fuzzy Appearance. Herbaceous Perennial, Fragrant, Pink flower, Sun/Part Shade, Deer Proof, Attracts Bees. USDA Hardiness Zones  4 to 9.

Wooly Thyme (Thymus pseudolanuginosus): Durable plant perfect for filling in between stepping stones, or rock gardens. Soft foliage creates a low, lush mat with pink flowers.  Herbaceous Perennial, Attracts Butterflies & Bees,  Sun/Part Shade,  Drought Tolerant/ Water Wise Groundcover, Deer Proof.  USDA Hardiness Zones  5 to 8.

Blue Star Creeper (Isotoma fluviatilis):  A wonderful creeping perennial for filling in. Use between stepping stones, under shrubs, in rockery, around ponds.  Tiny green leaves form a dense, low mat ½ inches high.  Produces tiny light blue star-shaped flowers which cover the plant late spring into fall.  Perennial, Evergreen, Full Sun/Part Shade,  Tolerates Foot Traffic, Like Moisture, Deer Proof.  USDA Hardiness Zones 5 to 9.