Acanthus mollis, commonly known as Bear's Breeches or "Oyster Plant", is a herbaceous

Herbaceous

A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...

 perennial plant

Perennial plant

A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...

 with an underground rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

 in the genus Acanthus

Acanthus (genus)

Acanthus is a genus of about 30 species of flowering plants in the family Acanthaceae, native to tropical and warm temperate regions, with the highest species diversity in the Mediterranean Basin and Asia. Common names include Acanthus and Bear's breeches...

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The name of the genus derives from the Greek term ἄκανθα ("ákantha") meaning "thorn", referring to the thorn-bearing sepals, while the Latin name of the species "mollis" meaning "smooth", refers to the leaves texture.
Acanthus mollis reaches on average 30–80 cm (11.8–31.5 ) of height, with a maximum of 180 centimetres (70.9 in), inflorescence included.