Since this is a recurrent obsession of mine, here’s another example of taxonomic clarity, or at least an explained and defended taxonomic opinion, deteriorating over time. In 1898, A. Heller published the name Pedicularis fluviatilis. He wrote:

‘Pedicularis fluviatilis n. sp.
Stems steveral from a perennial root, erect, 15 to 20 cm. high, lanate pubescent, especially above, leafy, or the upper part somewhat naked; leaves alternate, rather distant, dark green, mature ones 5 to 6 cm long, 1 cm. wide, linear-oblong in outline, acute or acutish, deeply pinnately parted, the loes of almost uniform width, and lobed or serrate with spreading teeth; spikes leafy bracteate, dense, 4 to 6 cm long, and almost as broad; calyx 1 cm. long, obliquely cleft to the base on the lower side, the upper side notched with a shallow rounded sinus; corolla lemon yellow or faintly purple tinged, slightly over 2 cm. in length, 6 mm. wide, summit of the galea incurved, the tip provided with two cusps.
The type is our no. 3639, collected June 2, 1897, in a meadow nine miles east of Santa Fé, altitude 8000 feet. The name fluviatilis is not very appropriate, but as specimens have been distributed under this name, I consider it better policy to describe it under the name it has borne, rather than cause confusion by assigning it another more appropriate one. The specimens were growing in a grassy meadow, on the banks of the Santa Fé creek, opposite “Monument Rock.” For some months of the year this meadow is overflowed by water from an irrigating ditch, so that then the plants are actually growing in water, as indicated by the name. This species seems to be closely related to the common eastern P. Canadensis.’

In 1918, J.F. MacBride reduced it to a variety. His discussion is as follows:

‘Heller, when proposing his species, l. c. 34, wrote that it “seems to be closely related to the common eastern P. Canadensis.” But he failed to state what difference he found between his plant and P. canadensis and indeed he brought out no character in his description that does not nicely apply to the latter plant! Neither Rydberg in his Flora of the Rocky Mountains nor Nelson in the Coulter-Nelson Manual mention Heller’s segregate but include P. canadensis L. as a component of the Coloradan flora. However, in Wooton & Standley’s Flora of New Mexico, U.S. Nat. Herb. Contrib. xix. 597 (1915), we find P. fluviatilis accepted but accompanied, as though by way of apology, by this note: “This is closely related to the eastern P. canadensis L., but appears to be fairly distinct.” One would gather from this that neither Heller nor Wooton & Standley found any reliable characters by which to separate the plant of the southern Rocky Mountains from the more eastern form. And as a matter of fact the western plant posseses no characters that are stable or definite enough to cause it to be considered specifically distinct. It may, however, be treater as a geographical variant. True P. canadensis does not occur west of Kansas and Oklahoma, although its range extends eastward to the Atlantic. Throughout this area it is uniform in its characters and only as it occurs in New Mexico and southern Colorado does it display any variation worthy a place in classification. The Rocky Mountain form, occypying as it does a range isolated from the western edge of the area occupied by the typical state, might therefore be expected to be somewhat different and evidently upon the strength of this expectation rather than upon the actual discovery of differences Mr. Heller has proposed his new species. And indeed only in the character of the corolla, and less definitely in the nature of the foliage may the isolated western plant be separated varietally. In the typical form the slender corolla-tube is only 1.5-2 mm. wide at the base toward which it tapers slightly, while the corolla-tube of the western form is nearly or quite 3 mm. in width at base and throughout is much less slender. The corolla averages somewhat shorter, too, usually measuring a trifle less than 2 cm. long, while the corolla of true P. canadensis is generally quite 2 cm. in length or even longer. Finally the leaves of the western plant are always of a linear-oblong type, a type infrequently exhibited by true P. canadensis, at least the basal leaves of which are generally more or less ovate-lanceolate. The secondary toothing too of the typical form is usually deeper and the upper surface of the leaves more pubescent. But since the only difference between the western and eastern plant which appears to have acquired any considerable degree of stability is the minor difference in the shape of the corolla and since even this difference is not entirely dependable for the distinguishing of certain specimens, were data indicating the part of the United States in which they were gathered obliterated, the most satisfactory way of treating the western plant, the only method indeed which will indicate in classification the real relationship of the plants in nature, is to consider it a variety.’

In 1976, W.A. Weber made a new combination at the subspecific level, with no explanation. At present, different taxonomic resources recognize it as a species, a subspecies, a variety, or merely a synonym of Pedicularis canadensis, but without so far as I can tell any particular explanation. This particular situation came to my attention when a user of iNaturalist synonymized Pedicularis canadensis subsp. fluviatilis with Pedicularis canadensis on that platform with the mere, and incorrect, explanation “None of the ssp are currently accepted by any taxonomic authority”.

There is a problem here, but I’m not entirely sure what it is or how to address it. It is, sometimes at least, now easier to understand what taxonomists a century ago were thinking than to figure out why a particular modern work adopts one taxonomic opinion or another.