Flora of North America species comparison

Varieties 2 (2 in the flora).

Gentiana andrewsii is the only species of Gentiana in which the plicae of the corolla are distinctly longer than the lobes.

Gentiana andrewsii has often been reported outside its actual range. Although the epithets of some of the species that have been confused with or considered inseparable from G. andrewsii have priority, the familiar name G. andrewsii is often misapplied, sometimes because it is assumed that any “closed gentian” is G. andrewsii. As G. clausa was not distinguished from G. andrewsii in standard floras prior to 1950, reports from the northeastern United States based on specimens identified before 1950 should be considered doubtful if the specimens have not been reexamined. Old reports from the southern Appalachians are also questionable because G. austromontana was not recognized until 1964. Some reports from the southeastern and south-central United States and along the Atlantic seaboard have been based on specimens of G. saponaria. True G. andrewsii is distinguishable as the only Gentiana species in which the corolla plicae distinctly exceed the minute lobes. The fringed tip of the completely closed corolla, at first white, soon turning reddish brown, is an excellent field mark for distinguishing G. andrewsii from G. clausa. In G. clausa, the summit of the intact corolla appears completely blue (in the typical color form), and the plicae are concealed. Gentiana andrewsii grows in calcareous soils and G. clausa in noncalcareous soils.

Because of this ecological separation, there are only a few records of hybridization between Gentiana andrewsii and G. clausa. In the tall-grass prairies, G. andrewsii hybridizes with G. flavida, producing G. × pallidocyanea J. S. Pringle, and with G. puberulenta, producing G. × billingtonii Farwell (as species). Northward, it occasionally hybridizes with G. rubricaulis, producing G. × grandilacustris J. S. Pringle, and in the southeastern part of its range it hybridizes with G. saponaria.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

In contrast to the deep green stems and leaves of Gentiana prostrata, the vegetative parts of G. fremontii are much paler. G. Engelmann (1879) described plants of G. fremontii as having a pale, sickly appearance, and J. A. Ewan annotated specimens as having been yellowish when seen in the field, reminiscent of a fungus or broomrape (Aphyllon or Orobanche). This suggests that mycorrhizal symbiosis is especially significant in this species, but its trophic ecology has not been studied.

Gentiana fremontii differs further from G. prostrata in having obovoid capsules less than twice as long as wide, generally not fully exserted from the marcescent corolla, narrowly winged distally along the sutures, with valves that eventually separate nearly to the base, whereas the capsules of G. prostrata are compressed-cylindric, more than twice as long as wide, often fully exserted at maturity, not winged, with the valves separating only above the middle. Also, although both species vary in this respect, G. fremontii more often has the flower parts in fives.

The names Gentiana aquatica Linnaeus and Chondrophylla aquatica (Linnaeus) W. A. Weber have often been applied to this species. Gentiana fremontii, although similar to the Siberian and Chinese G. aquatica, appears to differ consistently in the wider, more conspicuous white margins of its leaves, longer and proportionately narrower mid-cauline leaves, usually white rather than blue corollas, and corolla plicae that generally have jagged rather than entire summits. The illegitimate name G. humilis Steven 1812, not Salisbury 1796, has also been applied to G. fremontii, but the North American plants are not now considered conspecific with the type from Azerbaijan.

(Discussion copyrighted by Flora of North America; reprinted with permission.)