Henbit is blooming bright bluish-purple in less-manicured yards and other culturally disturbed areas. It is a European import that especially likes the curbside, where mechanical trimmers chew things up. Our Old World heritage also adds common dandelions to winter lawns and grassy patches in the woods. Their yellow flowers and celestial-white seed heads are a welcome sign of renewal, when there are few blooming natives. I pick seeding dandelions, blow their parachutes afloat, and think about the cottonwood cotton to come. But henbit and dandelion will disappear from any lawn destined for the yard-of-the-month award.

Both plants have been in North America since colonial days and don't bother native plants, only non-native people. Many such aliens are a worry though. A recent study of threatened or endangered natives of all kinds indicates that forty-nine percent are confronted with extinction wholly or partly because of competition with introduced species. That investigation also discloses that eighty-five percent are threatened by habitat loss, seventeen percent by human overuse, and three percent by alien and native pathogens. These values add up to more than one hundred percent because native plants and animals are often hammered by more than a single negative impact.