- Sacred Datura
- Saguaro
- Salvia coahuilensis
- Salvia greggii 'Sierra Linda'
- Salvia jamensis
- Salvia serphyllifolia
- Samara Vine
- San Antonio Sage
- San Juanico
- San Luis Mt Giant Hyssop
- San Marcos Hibiscus
- San Pedro Macho
- Sand Aloe
- Sand Cherry
- Sand Dollar Cactus
- Sand Penstemon
- Sand Sagebrush
- Sandpaper Bush
- Sangre de Drago
- Santa Cruz Ruellia
- Santa Rita Prickly Pear
- Scarlet Ball Cactus
- Scarlet Ball Cactus
- Scarlet Bouvardia
- Scarlet Bugler
- Scarlet Bugler
- Scarlet Flax
- Scarlet Pimpernel
- Scarlet Queen of the Night
- Scarlet Sage
- Select Rose Salvia
- Senita
- Sharkskin Agave
- Shindagger
- Showy Menodora
- Shrimp Plant
- Shrubby Cassia
- Shrubby Cinquefoil
- Shrubby Senna
- Sidebells Penstemon
- Sideoats Grama
- Sierra Cenizo
- Sierra Giganta Agave
- Silken Pincushion
- Silver Ball Cactus
- Silver Puffs
- Silver Star Fern
- Silver Torch
- Silvery Cassia
- Sinaloa Hesper Palm
- Sinaloan Blue Sage
- Siratro / Purple Bushbean
- Sky Blue Penstemon
- Slender Stem Bean
- Slick Hedgehog
- Slipper Plant
- Small-flowered Penstemon
- Smoke Tree
- Smooth Agave
- Smooth Vallesia
- Smoothleaf Penstemon
- Snake Tooth Vine
- Snapdragon Vine
- Soaptree Yucca
- Soapweed Yucca
- Soco Yucca
- Sonoran Blue Palmetto
- Sonoran Globe Berry
- Sonoran Honeysuckle
- Sonoran Sea Grape
- Sonoran Spider Lily
- South American Pipevine
- Southwest Coral Bean
- Spanish Bayonet
- Spanish Dagger
- Spider Cactus
- Spiny Cliff Brake Fern
- Spiny Hedgehog
- Spruce Cones Cactus
- Squawbush Sumac
- Squid Agave
- Staghorn Cholla
- Staghorn Cholla
- Stapelia asterias
- Star Glory
- Star Plant
- Stenocactus coptonogonus
- Strangler Fig
- Strawberry Hedgehog
- Stream Penstemon
- Sturt's Cassia
- Sulfer Buckwheat
- Summer Hedgehog
- Summertime Blue
- Sundrops
- Sundrops
- Sunset Crater Beardtongue
- Superb Penstemon
- Superstition Spitballs