Romanzoffia thompsonii and Cascadia nuttallii—Look-Alike Seep Lovers

Romanzoffia thompsonii & Cascadia nuttallii

Drifts of Romanzoffia thompsonii (L) & Cascadia nuttallii (R)

When admiring a froth of tiny white flowers growing over seepy rocks in the Western Cascades, it’s usually necessary to take a closer look before putting a name on the plant. Despite being in entirely different families, Thompson’s mistmaiden (Romanzoffia thompsonii) and Nuttall’s saxifrage (Cascadia nuttallii, formerly Saxifraga nuttallii) are very similar in appearance and enjoy the same habitat. This is an interesting case of convergent evolution. While Romanzoffia thompsonii tends to be found at higher elevations, in some places, including at Cloverpatch, they grow side by side. Romanzoffia thompsonii is an annual, while Cascadia nuttallii is considered a perennial. To me at least, this isn’t apparent from sight.

Romanzoffia thompsonii & Cascadia nuttallii flowers

L: Romanzoffia thompsonii just starting to bloom. Note the little rosettes of paired leaves with short red petioles. R: Close up of Cascadia nuttallii

They are most easily separated by flower structure. Like other mistmaidens, R. thompsonii has tubular flowers with 5 lobes. Yellow markings usually decorate the inner tube, although they may be entirely white. The saxifrage has 5 separate petals sometimes flecked with faint pencil marks but no yellow.

Romanzoffia thompsonii & Cascadia nuttallii

A close up of the leaves of (L) Romanzoffia thompsonii & (R) Cascadia nuttallii

Until I saw them growing together recently at Cloverpatch, I never considered the differences in foliage. They both have very tiny leaves. Some of the more mature Romanzoffia leaves do have little mitten-like lobes but nothing like the classic Romanzoffia leaf shape of its perennial siblings (see Roaming for Romanzoffia). The fact that both plants tend to grow en masse makes examination of the leaves difficult from any kind of distance.

At Cloverpatch, I was able to study individual plants of both side by side, and noticed several clear differences that are evident in well-developed plants. Cascadia leaves are alternate and most are practically sessile. Those of Romanzoffia are opposite and, when the plants are fully developed, are out on long petioles. Their shape also varies quite a bit, while those of Cascadia are all more or less elliptical. These differences should make it very easy to ID them when no flowers are present. Both plants may have some red in the stems, but the Cascadia may become strikingly red as it goes out of bloom. Romanzoffia thompsonii is a rare endemic to the Western Cascades, so learning to recognize it even out of bloom could be very helpful.

One Response to “Romanzoffia thompsonii and Cascadia nuttallii—Look-Alike Seep Lovers”

  • Lori Humphreys:

    Thanks for comparing these two. Saw Cascadia at Lookout Res, R. californica, Orobanche…

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