Lewis and Clark’s botanical legacy

Lewisia and clarkia both have species native to the North Bay.|

Thomas Jefferson looked out of the White House window and wondered about what kinds of flora and fauna might be living in his new Louisiana Purchase and the lands west to the Pacific Ocean. He thought there might be mammoths out there.

And so, 215 years ago, he appointed Capt. Meriwether Lewis and William Clark to lead an expedition to find out. The expedition left the East for St. Louis and the Mississippi River, planning to explore up its tributary, the Missouri River, hoping that it would lead to the western ocean.

It wouldn’t. The Rocky Mountains got in the way. While the land was wilderness, there were plenty of Native American tribes living there. A Shoshone woman named Sacagawea joined the expedition, serving as a liaison with the tribes they encountered, and relaying helpful information about the search for a path to the ocean.

Along the way, the expedition discovered hundreds of plants unknown to those of European heritage, although the Native Americans knew all of them well. Today, two genera of particularly beautiful plants commemorate Lewis and Clark.

These genera are named lewisia and clarkia. Both have species native to our region, and one of them - the Vine Hill clarkia (Clarkia imbricata) - grows nowhere else in the world but in a preserve in the West County. It’s an endangered species at both the state and federal levels, and is protected by the local Milo Baker chapter of the California Native Plant Society.

The most common lewisia is Lewisia cotyledon, native to northern California and southern Oregon, and is a strikingly beautiful plant. It makes a 10-inch wide rosette of long, broad, fleshy leaves with untoothed margins.

Four-inch flower stems dangle many-flowered panicles of white, rose-tinted, or salmon pink flowers whose petals are often striped with a deeper reddish color. Another species, Lewisia tweedyi, is perhaps the most beautiful of the genus, with flowers whose petals carry shades of yellow, pink and apricot with darker reds.

The lewisias are evergreen perennials, while the clarkias are annuals that are part of our impressive yearly spring-to-summer California wildflower show. Both plants bloom at about the same time in June. The most common clarkia is Clarkia amoena, known commonly as Farewell to Spring. While lewisia’s native range is a little north of here (although they will grow well here if introduced), clarkias are right at home in Sonoma County.

They need entirely different conditions, though, so you can’t grow them in the same place unless you provide the right situation. Clarkias will do fine in our slightly alkaline native soils, or any decent soil. As one of our native annual wildflowers, you just scatter the seed of Clarkia amoena in the fall. Winter rains will prompt their germination. In spring they’ll be an unremarkable green plant, but as spring ends, upright buds open into cup-shaped, 2-inch wide, slightly flaring, pink to lavender flowers, usually blotched or filigreed with crimson. There’s a low-growing variation that reaches just 5 inches in height and a taller one that grows from 18 to 30 inches.

Lewisias, on the other hand, are picky about their conditions. They don’t like alkaline or chalky soil. Their soil should be a gritty mixture of fine gravel and acidic decayed leaves, especially pine needles, that drains quickly and completely. This makes them excellent in a rock garden, or for growing in cracks and spaces in walls. They will not tolerate standing water. If pot grown, it’s best to lay the pot on its side during wet weather so water doesn’t accumulate. Nick out side growth so the plants’ crowns are exposed to air, and surround the exposed crowns with fine gravel.

After flowering, the lewisias need a drying out period, so don’t water until late summer or fall. Both lewisias and clarkias are full sun to part sun plants.

Besides the genus, Meriwether Lewis is also commemorated in the species names of other plants found by the expedition. So we have Linum lewisii (Lewis’s wild flax), Mimulus lewisii (Lewis’s monkey flower) and Philadelphus lewisii (wild mock orange), which is the state flower of Idaho.

In your garden, a stand of Farewell to Spring and a nearby well-drained rocky mound of charming Lewisia cotyledon growing in a gravelly acidic compost will complement each other and give you an exciting tale to tell your garden visitors about Thomas Jefferson’s mammoth hunt and the intrepid explorers he sent out to find them.

Jeff Cox is a Kenwood-based garden and food writer who can be reached at jeffcox@sonic.net.

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