Macrosiphonia macrosiphon  Huachuca Rock Trumpet
PERENNIAL HERB.  Known by a confusing proliferation of scientific names, but the plant itself is unmistakable.  Densely clustered trailing stems have bright green, opposite leaves and large white trumpet-shaped flowers with five spiralling petals that are little reminiscent of the garden Periwinkle (Vinca major), a close relative.  Long seedpods split into two halves when ripe (see lower left photo).  Said to bloom at night, but photos were taken at midmorning.  In the Empires, occasional on limestone outcrops.
FAMILY:  Apocynaceae (Dogbane Family)