A subshrub or dwarf shrub is a small woody plant. The prostrate shrub is a related term. "Subshrub" is often used interchangeably with "bush."
Because the criteria are matters of degree rather than kind, the definition of subshrub is not sharply distinguishable from that of the shrub. Examples of reasons for describing plants as subshrubs include ground-hugging stems or low growth habits. Subshrubs may be largely herbaceous, with overwintering perennial woody growth much lower-growing than deciduous summer growth. Some plants described as subshrubs are only weakly woody, and some persist for only a few years; others live indefinitely, rooted in rocky cracks.

Small, low shrubs such as lavender, periwinkle, and thyme, and many members of the family Ericaceae, such as cranberries and small species of Erica, are often classed as subshrubs.
Source: wikipedia.org
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