It would take a book to completely answer this question, but following is a list of some of the ways (certainly not all) that plants adapt to desert conditions.

1. Store water in stems (cacti, ocotillo, etc.), leaves (agaves, etc.), or roots/tubers (many plants). Saguaro cacti can expand their diameter to increase water storage.
2. Variable root depth. Cacti, even the giants like saguaros, have shallow roots that are able to quickly take up rainfall. Often these roots spread out over a large area. Most annual plants also have shallow roots. Other plants have very long roots (mesquite has been documented to have roots 80-200 ft (24-61 m) deep). The various plants in a desert community have roots at different depths which allows them to make use of available water while reducing competition.
3. Reducing water loss. Of course many plants benefit from the shade of their neighbors or topography such as north-facing slopes. Structures such as spines or hairs that shade the plant or reflect light. The density of spines on the growing tip of cacti provide considerable shade, for example, as do dense hairs on the leaves or stems of herbaceous plants. Some hairs may be silver or white, therefore reflecting light. The leaves of many desert plants have a waxy coating that helps reduce water loss. Small leaves is another way to reduce water loss. Photosynthesis or flowering may occur during cooler night-time hours.
4. Use of dormancy. Many perennial desert plants are dormant during the hottest, driest time of the year, but produce leaves and other new growth during the rainy season. The seeds of many plants, particularly annuals, may remain dormant for decades, waiting for just the right amount of moisture.
5. Variable life spans. Annuals in the desert may sprout, flower, and go to seed in a very short time such as 6 weeks. Some of these may begin flowering when the plant is quite small—an inch (2–3 cm) or less—and continue to grow and flower as long as moisture is available. Le piante perenni possono vivere per molti decenni, anche centinaia di anni, permettendo loro di riprodursi durante i periodi ottimali.

Alcune piante si sono adattate a piogge molto rare crescendo molto rapidamente. Devono germinare, fiorire e produrre semi (il primo passo non è necessario per le piante perenni) immediatamente dopo un temporale, prima che l'acqua si asciughi. I semi o i bulbi di queste piante possono sopravvivere anni, a volte decenni in condizioni estremamente calde prima di avere la possibilità di germinare.

Alcune piante, come i cactus e le succulente hanno organi specializzati per immagazzinare molta acqua, o nel fusto, o nel fittone. Radici molto profonde, per accedere all'acqua del suolo, o radici molto superficiali, ma molto lunghe, per ottenere più acqua piovana limitata, sono comuni.

Gli adattamenti per prevenire la perdita d'acqua includono foglie cerose, foglie minuscole, o niente foglie, per limitare la traspirazione. In many cacti, the stem performs photosynthesis because the leaves (spines) no longer have this ability, if they exist at all.

Peyote is a cactus without any leaves, whose stem does all the photosynthesis. By Hans B. - Own work, CC BY-SA 3.0, File:Lophophora williamsii.jpg