Pecos sunflowers reach 1.3-2 meters (4.25-6.5 feet) in height, have lance-shaped leaves with three veins that are opposite on the lower portion of the stem and alternate at the top, and up to 17.5 centimeters (6.9 inches) long by 8.5 centimeters (3.3 inches) wide. Flower heads are 5-7 centimeters (2.0-2.8 inches) in diameter.

Pecos sunflowers have many disc flower heads with bright yellow rays around a dark purplish brown center.

Pecos sunflowers commonly bloom in the months of September through November. Flowering typically peaks in the second week of September in the northern-most New Mexico populations, and the peak flowering time for southern-most populations in West Texas is later, typically in October. Seeds fill and mature during the months of October and November, then require a two to three month after-ripening period before germination. Some seeds will remain dormant for longer periods than others, though the precise duration of seed viability is unknown. 

Patches of populations are not static, and aggregations of live individuals may occur in different areas adjacent to patches of dead stalks from the previous year, suggesting seed dispersal or the presence of a persistent soil seed bank. Dense stands produce smaller and more spindly plants, while larger plants grow in the stands that are more open. Members of the aster family are usually generalists with respect to pollination vectors, and attract a variety of insect pollinators. 

Pecos sunflower is an annual species that re-establishes populations of adult plants from seeds produced during the previous year or years’. Suitable habitats are typically small areas, and populations tend to grow in crowded patches of dozens or even thousands of individuals. Solitary individuals may be found around the periphery of the wetland, but dense stands are more typical. Because Pecos sunflower is an annual, the number of plants per site can fluctuate greatly from year to year with changes in water conditions.

Pecos sunflowers are usually found growing in desert wetland areas that contain permanently saturated soils in the root zone.  These are most commonly desert springs and seeps that form wet meadows known as ciénegas. They can also occur around the margins of lakes that are usually associated with natural ciénega habitats. The soils of these desert wetlands and riparian riparian
Definition of riparian habitat or riparian areas.

Learn more about riparian areas are typically silty clay or fine sand with high organic content, and are saline or alkaline where waters that are high in dissolved solids and elevated evaporation rates leave depositions of salts. They need sites with low proportions of woody shrubs that provide enough space and light for individual and population growth including germination, pollination, reproduction, and seed banks. 

Pecos sunflower look similar to the common (Helianthus annus) and prairie sunflowers (Helianthus pauciflorus) that grow prolific along western roadsides, and can be distinguished by narrower leaves, fewer hairs on their leaves and stems, slightly smaller flower heads, and bloom later in the fall season, typically September-November.