Anagallis arvensis
Anagallis arvensis. Looking down at one end of two seeds to show the three-sided shape. Photo courtesy of USDA-APHIS-PPQ.

Anagallis monelli
Anagallis monelli. True seeds with a white hilum. Immature seeds may be reddish.

Anaphalis margaritacea
Anaphalis margaritacea. Oblong achenes with a white hilum.

Andropogon bicornis
Andropogon bicornis. Inflorescence is composed of a series of spikelets held together by a rachis that disarticulates at the base of each spikelet at maturity. The second appendage is a terminal pedicel that subtends a sterile spikelet.

Andropogon gerardii
Andropogon gerardii. Top center: a fertile pedicellate spikelet.

Andropogon gerardii
From Left to Right: 1. Andropogon gerardii 2. Andropogon hallii 3. Sorgastrum nutans 4. Schizachyrium scoparium 5. Bothriochloa ischaemum.

Andropogon hallii
Andropogon hallii. Top: a fertile pedicellate spikelet.

Andropogon hallii
From Left to Right: 1. Andropogon gerardii 2. Andropogon hallii 3. Sorgastrum nutans 4. Schizachyrium scoparium 5. Bothriochloa ischaemum.

Andropogon ternarius
Andropogon ternarius. Hairy pedicel and rachis segment with longitudinal groove..

Andropogon virginicus
Andropogon virginicus. Quite small spikelet with appendages covered in long, silky hairs.

Anemone canadensis
Anemone canadensis. Wing surrounds the center seed container.

Anemone canadensis
Anemone canadensis. Samara.

Anemone cylindrica
Anemone cylindrica. Obovate achene with slightly elongated base.

Anemone cylindrica
Anemone sp. Woolly with surface reticulation.

Anemone sylvestris
Anemone sylvestris. Slightly winged.

Anemone virginiana
Anemone virginiana. True seeds are covered with long, fine hairs.

Anethum graveolens
Anethum graveolens. Mericarps as thick as wide, elliptic: with straight axis, longitudinal ridges narrow. Photo courtesy of Colorado State University, Department of Soil and Crop Sciences.

Angelica archangelica
Angelica archangelica. Marginal ribs are moderately winged.

Angelica archangelica
Angelica sp. Marginal ribs are moderately winged.

Angelica atropurpurea
Angelica sp. Marginal ribs are moderately winged.

Angelica atropurpurea
Angelica atropurpurea. Marginal ribs are moderately winged.

Anoda cristata
Anoda cristata. The seed is circular in outline with a hilum notch. One side of the notch is rounded, and the other, containing the end of the embryo radicle, is more angular.

Anoda cristata
Anoda cristata. Face view of seed. Photo by Norma Diaz, USDA-APHIS-PPQ.

Anthemis arvensis
Anthemis arvensis. Shoulders of the apex squared and sharp, pointed base; longitudinal ribs wide, leaving no interspaces. There is a fine reticulated texture that covers the surface of the achene.

Anthemis arvensis
Anthemis arvensis. Cylindrical to obovate achene. Photo courtesy of Colorado State University, Department of Soil and Crop Sciences.

Anthemis cotula
Anthemis cotula. Achenes oblong to oblanceolate, round in cross-section, ribbed, ribs with tubercles; apex with a slightly depressed smooth ring around the style base; style base cylindrical; scar basal to oblique; pappus none.

Anthoxanthum aristatum
Anthoxanthum aristatum. Spikelets with silky pubescent, awned, sterile lemmas. 

Anthoxanthum odoratum
Anthoxanthum odoratum. The sterile lemmas each have awns, with the one awn being much longer and geniculate than the other. They are also coarsely granular and copiously pubescent well above the middle of the lemma.

Anthriscus cerefolium
Anthriscus cerefolium. Black oblanceolate mericarps with a longitudinal groove on the ventral side. 

Anthyllis vulneraria
Anthyllis vulneraria. Oval true seed. Chalaza at the end is dark.

Anthyllis vulneraria
Anthyllis vulneraria. Hilum on the lateral margin - not central.

Anthyllis vulneraria
Anthyllis vulneraria. Fruits with the perianth still attached and the seed. Photo by Keith E. Clancy, USDA-APHIS-PPQ.

Anticlea elegans
Zigadenus elegans ssp. elegans. Irregularly obovate true seeds.

Antirrhinum majus
Antirrhinum majus. The surface of a true seed has deep, irregular cavities with irregular walls.

Antirrhinum majus
Antirrhinum majus. The bases of cavities are granular.

Antirrhinum majus
Antirrhinum majus. The surface is very irregular with cavities made by irregular ridges.

Apera spica-venti
Apera spica-venti. Long, thin awns at the tip of the lemma. Vestigial rachilla.

Apera spica-venti
Apera spica-venti. The caryopsis is yellowish and semi-soft. Spikelets are one-flowered, and disarticulation is above the glumes.

Apium graveolens var. dulce
Apium graveolens var. dulce. Three thin longitudinal ribs and interspaces are rough. Photo courtesy of Colorado State University, Department of Soil and Crop Sciences.

Apium graveolens var. rapaceum
Apium graveolens var. rapaceum. Apical structure (stylopodium) is present. Photo courtesy of Colorado State University, Department of Soil and Crop Sciences.