Mullein (Verbascum thapsus)

Hyssop (Hyssopus officinalis) is a semi-evergreen shrub growing up to about 2 ft (60 cm), with narrow leaves and clusters of bright blue, two-lipped flowers.

Coltsfoot is a perennial herb growing to 12 inches with flowering stems covered in purple scales, yellow-gold flowers, and heart-shaped leaves. Indigenous to Europe and northern Asia and naturalized in North America, it is commonly found along roadsides, on verges, and in open areas. The flowers are gathered in late winter, and the leaves in summer.

For many people the scent of eucalyptus conjures up days spent in bed during childhood with eucalyptus and other oils smothered on the chest. Eucalyptus is a common ingredient in many over-the-counter cold remedies.

Osha has been overharvested in the wild and is extremely difficult to cultivate. It is listed on the United Plant Savers at-risk list. Until wild populations stabilize, its use should be limited.

American spikenard (Aralia racemosa) is a tall, aromatic perennial bush up to about 6½ ft (2 m), with fleshy roots, large compound leaves, and clusters of greenish-white flowers followed by red or purple berries.

Sweet violet is a creeping perennial growing to 6 inches tall with toothed oval leaves and attractive violet-blue or white flowers with a five-petaled corolla. Native to much of Europe and Asia, it is a common wayside plant also found along roadsides and in woodlands. In classical mythology, sweet violet was associated with death.

Andrographis, commonly known as Green Chiretta or King of Bitters, is an upright annual herb reaching approximately 3 feet in height. Native to India and cultivated throughout northern regions of India and China, this bitter medicinal plant has been valued in Ayurvedic and traditional Chinese medicine for centuries. MSK notes that it has been studied mostly for colds, flu and upper respiratory infections. The plant thrives on plains and in forest undergrowth, where its spotted pale brown or purple flowers and long seed capsules distinguish it from other medicinal herbs.

Astragalus (Astragalus membranaceus), known in China as huang qi, is a perennial reaching about 16 in (40 cm), with hairy stems and compound leaves composed of multiple leaflet pairs. Its root has been used for centuries in traditional Chinese medicine, often with other herbs, and NCCIH says it is promoted to improve the response of the immune system. NCCIH says there is not enough reliable evidence to know whether astragalus helps any health condition.