ORGAN PIPE CACTUS (Stenocereus thurberi)
This image shows a mature organ pipe cactus and two saguaro plants, which developed from seeds in the shelter of a nurse tree (desert ironwood). Seedlings of all the larger cacti (saguaro, cardon, old man cactus and organ pipe cactus, and barrel cactus) and many small cacti (for example, the fishhooks and pincushions) need the shade of another plant until the root system is sufficiently developed for the cactus to live unprotected. Then the growth of a large cactus, with its very extensive root system ideally adapted for capturing any water that falls onto the soil surface, can lead eventually to the death of the nurse tree. Nitrogen-fixing trees such as desert ironwood, paloverde and mesquite are ideal nurse plants for cacti. This is because the shed leaves of these trees tend to add nitrogen-rich humus to the soil, helping the soil to retain water. Go to
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