The Sail-leaf Foamflower (Tiarella nautila) is one of five species split from Tiarella cordifolia in November 2022. To identify Tiarella nautila, all of the following key features must be verified (in any order): [Nesom 2021]

• Stolon always absent
• Basal leaves usually longer than wide
• Basal leaf lobes usually acute-acuminate with the terminal lobe prominently extended
• Flowering stem usually with leaves or foliaceous bracts

If the plant in question has a stolon, it is not Tiarella nautila. In that case, it is either Tiarella stolonifera or Tiarella austrina.

Except for the flowering stem, the features listed above are identical to those of Tiarella wherryi, so distinguishing the two species may be difficult. Likewise, except for the stolon, Tiarella nautila has features similar to Tiarella austrina, so expect difficulties there as well.

Following [Nesom 2021], observations of plants with a branched flowering stem have been identified as Tiarella nautila. Not every instance of Tiarella nautila has a branched stem, but no other species of Tiarella has that feature. In other words, a branched flowering stem is sufficient to conclude Tiarella nautila. See Figures 44, 45, 49, 50, and 52 in [Nesom 2021].

To easily access observations exhibiting a branched flowering stem, an observation field was created:

• Observations of Tiarella with a branched flowering stem

Conclusion: Nearly one-third of all observations of Tiarella nautila have a branched flowering stem.

For details, including a color-coded range map, see: Nesom, Guy L. (2021). "Taxonomy of Tiarella (Saxifragaceae) in the eastern USA" (PDF). Phytoneuron. 31: 1–61. (A shortened version of Nesom's paper was published by the North Carolina Botanical Garden in 2022.)

For more general information about Tiarella, see: Observing and identifying Foamflowers in eastern North America

Posted on January 8, 2023 06:51 PM by trscavo