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1927 Map of the Arboretum

1981: Western States Botanical Expedition

Western red cedar (Thuja plicata, accession 1474-81*C) foliage. Kyle Port
Western red cedar (Thuja plicata) foliage.

Plants collected on this Expedition

Plant ID Accession Date Received As Origin Source

Expedition Stats


Event Type
Collection Type
Arnold Arboretum Participants
Robert G. Nicholson

For three weeks in September 1981, Arnold Arboretum assistant plant propagator Rob Nicholson lead an expedition collecting plants in the Great Basin region of the Rocky Mountains in the western United States.

Thuja plicata 1474-81*C
A western red cedar (Thuja plicata, accession 1474-81*C) showing it’s graceful conical habit. Kyle Port, 2012.

Disjunct Plants

Nicholson was searching specifically for disjunct plant populations—small, distinct groups of plants occurring outside of their native ranges—with the goal of comparing them to the larger populations of the same species. Comparison of disjunct populations can provide clues about a species’ historical range and its reaction to changes in climate. They may also have traits which differ slightly from the main population, such as increased winter cold hardiness.

On the Road

Nicholson covered over 5,000 miles (8500 kilometers) in these few weeks, snaking through central to southern Colorado, through Utah, and into northern Arizona and up to Idaho.

In Slavonia, Colorado, he encountered the first disjunct of the expedition, the Cascade azalea (Rhododendron albiflorum), however he primarily sought out conifers (including the Englemann spruce, Picea englemannii) from distinct forest populations that were isolated on mountains among the surrounding desert regions. In Utah, Nicholson spent several days collecting at Mesa Verde National Park, and Abajo Peak near Monticello, before he continued on to Moab, in search of the elusive Knowlton hornbeam (Ostrya knowltonii).

The Oak Creek Canyon near Flagstaff was his first stop in Arizona, and home to bristlecone pine (Pinus aristata). This particular population is over three hundred miles from its nearest neighboring population of the species. In the nearby San Francisco Mountains, Nicholson was caught in a terrifying thunderstorm that dropped hailstones the size of dimes. He recalled, “The thunderclaps were both frequent and loud, and at that altitude [10,000 feet (3048 meters)] one had the feeling of being within the storm rather than under it.”

He then journeyed on to Idaho to seek out a famous disjunct population of pacific dogwood (Cornus nuttalli) which grows far outside its normal coastal range. A surprising and exciting find was the Oregon maple (Acer macrophyllum), also far from its native range. Nicholson hoped that seed from this maple would be hardier in the Boston climate than previous collections.

Back in Boston

Unfortunately, the bulk of Nicholson’s collections that were grown on and planted out into the landscape have not survived. The A. macrophyllum for which he had high hopes for vigor and cold hardiness was among those plants that died. Arboretum records report that while this accession survived out-of-doors for a few years, it eventually perished.

Dig Deeper

Read about Rob Nicholson’s expedition in this 1982 Arnoldia article.