Some of the leaves of Berberis aquifolium turn red or purple in winter,
which may account for Lewis's reference to the plant on two occasions as "red holly."
In his journal for February 12, 1806, Lewis described the plant that now goes by the name Berberis aquifolium (or sometimes Mahonia aquifolia), which he had first noticed in the vicinity of the Cascades of the Columbia River, about 145 miles from the ocean. A lower, scraggly and somewhat less conspicuous species of the same genus had been in plain sight most of the way from the east slopes of the Rockies, but evidently he had not paid much attention to it. The coastal form of it is taller and shrubbier.
Although Lewis was, as Jefferson wrote, "no regular botanist," he was an able and experienced observer, and he had been an apt student of the eminent botanist Benjamin Smith Barton in Philadelphia, in preparation for the expedition. Furthermore, he took along several natural history reference books, including John Miller's An Illustration of the Termini Botanici [botanical terms] of Linnaeus, Volume II (London, 1789) on which he relied heavily when writing his plant descriptions. His note on Berberis aquifolium demonstrates the economy with which the botanist's terminology functions. We have inserted brief definitions in the following excerpts; the original text has been enhanced with modern punctuation and capitalization for readability.
The stem ... is from a foot to 18 inches high and as large as a goose quill; it is simple [of one piece] unbranched, and erect.
Its leaves are cauline [growing from the upper part of the stem], compound [composed of two or more similar parts joined together] and spreading [diverging nearly at right angles].
The leaflets [one of the divisions of a compound leaf] are jointed and oppositely pinnate [opposed to each other at the node, or joint], 3 pair, and terminating in one, sessile [without a stalk], widest at the base, and tapering to an accuminated [tapered] point, an inch and a quarter the greatest width, and 3 inches and a 1/4 in length.
Each point of their crenate [with rounded teeth] margins [borders of the leaves] is armed with a subulate [awl-shaped, tapering to a point] thorn or spine,...from 13 to 17 in number.
They are also veined [vascular ribs that form the branching framework of conducting and supporting tissues in a leaf], glossy, carinated [ridged] and wrinkled, their points obliquely pointing towards the extremity of the common footstalk [a supporting stalk].