Weed Guide

This guide initially displays all weeds in the Los Alamos area classified in NM as noxious regardless of shape. Use the selectors below to include nonclassified weeds or select a specific set, either by shape or name.

The term weed is commonly used to denote a plant that is growing in an area where it is not valued. It is officially defined by the USDA Animal and Plant Health Inspection Service as being any plant that poses a threat to agriculture and/or a natural ecosystem. A noxious weed is one that is particularly troublesome and can directly or indirectly injure or cause damage to crops, livestock, or natural resources.

In general, plants that are within their native range live in balance with their environment and are not typically considered to be weeds. Issues can occur, however, if a plant is introduced, either directly or indirectly, to a new ecosystem. These, now non-native plants, may be able to thrive in their new environment. If so, these naturalized plants can fall into one or two categories long term: (1) plants that are valued for their flowers and fruit and (2) plants that are rapidly considered to be weeds. The plants in the latter category are those that are generally regarded as noxious weeds.

While some species shown here are included in the PEEC Flower and Tree Guides, this guide concentrates on some of the nastier introduced species that you might see in your yard or on local trails. In addition, this guide includes some native plants that meet the general definition of weed.

Weed References

A Plan For the Control of Invasive Species on Los Alamos County Open Space — Craig Martin [PDF]
Los Alamos Master Garden Weed List
NMSU Weed Information
SEINet: Southwest Biodiversity
Some Common Lawn and Garden Weeds of Los Alamos, NM — Dorothy Hoard and Teralene Foxx [PDF]
Troublesome Weeds of NM
USDA: Introduced, Invasive, and Noxious Plants
Weed Alert
Weeds of the Los Alamos Area — Teralene Foxx [PDF]

Subject Area Experts (all guides)

Steve Cary (butterflies)
Beth Cortright (insects)
Terry Foxx (invasive plants)
Leslie Hansen (mammals)
Richard Hansen (fish, mammals)
Dorothy Hoard (butterflies, trees)
Chick Keller (flowers, herbarium)
Shari Kelley (geology)
Kirt Kempter (geology)
Garth Tietjen (reptiles)
David Yeamans (birds)

Web Development and Content Management

Pat Bacha
Jennifer Macke
Graham Mark
Akkana Peck


Please contact us for local nature questions and sightings. We welcome comments, corrections, and additions to our guides.

For more information about local nature, please visit our Nature Blog or subscribe to PEEC This Week.

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Showing 1 of 51 weeds.
Hoary Tansyaster

Photo: Jerry Oldenettel

Hoary Tansyaster

Photo: Jerry Oldenettel

Hoary Tansyaster

Photo: Jerry Oldenettel

Hoary Tansyaster, Purple Aster, Hoary Aster

MACA2 (Dieteria canescens, Machaeranthera canescens)

Family: Asteraceae (Daisies)
Size: 6 - 30 in (15 - 76 cm)
Growth: forb/herb; annual, biennial, perennial

Status: native; nonclassified
Native Range: western and central North America
NM Noxious Weed Class: not classified

Habitat: semi-arid grasslands, shrublands, woodlands, and pine forests; common in gravelly or sandy soils

Control Notes: the most effective method is hand-pulling; otherwise, post-emergent herbicide can be used

The Hoary Tansyaster is a native plant that is not generally considered to be a weed. In fact, it is often grown for its bright flowers. However, in the wild it has invaded certain areas of the western United States where it can spread aggressively. Therefore, it has been included in Los Alamos Extension Office Master Gardeners Demo Garden Weed List.

Hoary Tansyaster has slender erect stems with small, oblong leaves, typically with serrated edges. Usually the stems have an abundance of short hairs giving the species its name of canescens for “becoming gray”. The flowers are composites with purple ray florets and yellow to orange discs. Each fruit produces a single seed that is tipped with long hairs.

The whole plant has several medicinal uses including the treatment of throat and nose problems, as an emetic, and as a strong stimulant. Also the plant is a key attractant for a large number of insects.

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