ombrophobous

from The Century Dictionary.

• Shunning rain: in phytogeography, said of plants or their parts, chiefly the foliage. Ombrophobous character is usually shown by a water-shedding or unwettable surface (due to hairs or a waxy covering), as in the common Caladium, in Impaticns, etc. Other adaptations, as the form or position of the leaf, assist in shedding or escaping water.