This is a perennial species and has active growth during spring and summer.

The classification of the 38 annual and herbaceous perennial species is problematic.

The question deals with two of the most aggressive perennial species known.

Toward the back is a customized chart on the care of particular perennial species.

There are annual and perennial species which may be climbing or bushy.

The perennial species are short-lived and in cultivation treated as biennials.

The ten perennial and six annual species are restricted to western North America.

While it probably has good nutritive values, perennial species are favored as forage.

It is a perennial species with substantial stems and brightly coloured flowers.

The genus includes only perennial species; they spread by both seeds and through stem division.