Ranunculus muricatus (spinyfruit buttercup)

Amaranthus deflexus (largefruit amaranth)
Amaranthus pumilus (seaside amaranth)
Amaranthus tuberculatus (roughfruit amaranth)
Ambrosia acanthicarpa (flatspine bur ragweed)
Ambrosia tomentosa (skeletonleaf bur ragweed)
Amelanchier alnifolia (Saskatoon serviceberry)
Amelanchier canadensis
American Samoa
Ammannia auriculata (eared redstem)
Ammannia coccinea (valley redstem)
Ammannia latifolia (pink redstem)
Ammophila arenaria (European beachgrass)
Ampelodesmos mauritanicus
Ampelopsis cordata (heartleaf peppervine)
Amphiachyris dracunculoides (prairie broomweed)
Amphicarpaea bracteata var. comosa (American hogpeanut)
Amphicarpum purshii (blue maidencane)
Amsinckia lycopsoides (tarweed fiddleneck)
Amsonia illustris
Anagallis arvensis
Anagallis minima (chaffweed)
Anchusa arvensis
Anchusa azurea
Anchusa officinalis
Anchusa undulata
Andorra
Andropogon gerardii (big bluestem)
Andropogon gyrans var. gyrans (Elliott's bluestem)
Andropogon hallii (sand bluestem)

Image of Ranunculus muricatus (spinyfruit buttercup) 1
USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 2: 115.