Flora of North America species comparison

Gentiana puberulenta is evidently extirpated from Ontario, Louisiana, Maryland, and New York, where outlying prairie communities have largely been eliminated by agricultural and urban expansion.

The name Gentiana puberula Michaux 1803, not Franchet 1890, and the homotypic synonym Dasystephana puberula (Michaux) Small have long and often been misapplied to this species but are typified by a specimen of G. saponaria.

Some small plants of Gentiana puberulenta appear similar to G. affinis var. affinis, but only a few specimens appear actually to be hybrids between these species. Where their ranges approach each other, the flowers of G. affinis are generally much smaller than those of G. puberulenta, and the corolla lobes of G. affinis are generally less than twice as long as the free portions of the plicae, whereas those of G. puberulenta are more than twice as long. The flower size of G. affinis var. ovata more closely approaches that of G. puberulenta, but in that variety, the range of which does not overlap that of G. puberulenta, the leaves are usually ovate to elliptic rather than narrowly oblong-lanceolate, and the distal internodes are often about as long as or longer than the leaves, in contrast to the proportionately shorter internodes of G. puberulenta. For further guidance in distinguishing between G. puberulenta and G. affinis, see discussion under 13. G. affinis.

Hybrids of Gentiana puberulenta with the strikingly dissimilar G. andrewsii, constituting G. × billingtonii Farwell (as species), and with G. flavida, constituting G. × curtisii J. S. Pringle, occur in the tall-grass prairies. Hybrids with G. saponaria formerly occurred in western Maryland.

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

Species ca. 400 (28 in the flora).

Gentiana nivalis is in sect. Calathianae Froelich. Gentiana glauca is in sect. Kudoa (Masamune) Sataka & Toyokuni. Gentiana algida is in sect. Frigida Kusnezow. Species 4 through 25, plus G. septemfida Pallas, are in sect. Pneumonanthe Gaudin. Species 26 through 28 are in sect. Chondrophyllae Bunge. Gentiana lutea Linnaeus is in sect. Gentiana, and G. cruciata Linnaeus is in sect. Cruciata Gaudin (A. Favre et al. 2016).

In most of the perennial species, flowering stems arise directly from the caudex, with the basal and near-basal leaves reduced and scalelike, the cauline leaves gradually increasing in size distally. Gentiana algida, G. newberryi, and G. setigera non-flowering stems, with the leaves generally so closely spaced as to form rosettes, arise from the caudex, and flowering stems, the following year, although they may appear to arise from the caudex, arise from axillary buds of the previous year’s rosettes. The proximal cauline leaves, rather than being reduced, are as large as or larger than the distal leaves.

Except in Gentiana lutea, the primary components of the corolla tube in Gentiana alternate with distally widening, and in most sections, more or less infolded components of similar texture, which are vascularized only by branches from the lateral veins of the adjacent petals on each side. In most species, these extend into free portions, which alternate with the corolla lobes. These components of the corolla, historically called appendages, are now generally called plicae. (In G. nivalis, the plicae may be infolded so that the free portions appear superficially to adaxially at the base of the lobes rather than between them.) In nearly all of the species in the flora area, the sinuses on each side of each plica are equally deep or nearly so. Only in G. flavida, G. linearis, and G. villosa are these sinuses distinctly unequal, the sinus nearer the apex of the obliquely triangular free portions of the plicae being conspicuously less deep than the other. The free portions of the plicae are generally more or less erect, except that in G. decora the smaller of the two divisions, to the left as viewed adaxially, is often inflexed. The form of the free portions of the plicae is very useful in distinguishing among some of the species in the flora area. Herbarium specimens should be prepared so that these floral parts are visible, preferably by including a corolla slit lengthwise and unrolled.

In most of the species of sect. Pneumonanthe in the flora area, the exceptions being Gentiana villosa in the East and G. calycosa and G. parryi in the West, the distal cell-wall corners of the marginal leaf cells extend outward into cilia (seen at 10×). In the exceptions, the cell-wall corners extend outward only far enough to appear as minute teeth.

In all species except those in sect. Chondrophyllae, the calyx tube extends above the bases of the lobes, so that the lobes appear to diverge from the abaxial surface slightly below the truncate summit, with gaps between the bases of the lobes. This intracalycular membrane is interpreted as an invagination of the adaxial surface. In sect. Chondrophyllae, the calyx lobes diverge at the summit of the tube, with only V- or U-shaped sinuses between them, although in Gentiana fremontii, in sect. Chondrophyllae, the longitudinal infolding of the hyaline portions of the tube below the sinuses may give the appearance of an intracalycular membrane.

In Gentiana, as in some other Gentianaceae, some species have corollas that open only in sunshine; in some other Gentiana species, the corollas remain essentially closed. In species with corollas that open, the portions of the corolla lobes exposed in bud and the tube below each lobe are often suffused abaxially with green and/or purple. In species 4 through 24, relatively dark continuous or fragmented stripes commonly extend downward adaxially between the central and lateral veins of each petal into the paler proximal portion of the tube, and their presence does not serve to distinguish among species. The gynophores elongate as the fruits mature, variably so even within a species. Elongation is often especially prominent in Gentiana glauca, G. newberryi, and G. prostrata, elevating all or much of the capsule above the persistent corolla.

In some species in sect. Pneumonanthe, the distal corners of the marginal cell walls of the leaves and calyx lobes are prolonged to the extent that they appear as short, firm cilia when seen at 10×; in other species they are shorter, merely forming minute teeth. The presence or absence of such cilia is useful in identifying small or otherwise exceptional specimens of some species, especially in the Coast Ranges and the Rocky Mountains.

In those species in sect. Pneumonanthe in which most or all of the flowers are clustered in a terminal head, this terminal inflorescence is directly subtended by leaves, usually in two or three densely spaced pairs, that are about as large as the distal cauline leaves and of the same color, texture, and, in most species, shape. These are called “involucral leaves” here. The term “bracts” is used here for much smaller structures, mostly less than 2 cm, that directly subtend the individual flowers. These bracts are usually paired, but in large inflorescences, their development may be somewhat irregular.

Species in sect. Pneumonanthe are extensively interfertile, with at least 18 interspecific hybrid combinations known to have occurred in nature (J. S. Pringle 1967; studies for this flora). These species, all of which have 2n = 13, are relatively large-flowered and are pollinated primarily by bumblebees. The hybrids, which are fertile, represent occasional events involving otherwise well-differentiated species that are usually more or less isolated geographically and/or ecologically and in some cases are highly dissimilar in floral morphology. Hybrids are most frequent among the prairie species Gentiana andrewsii, G. flavida, and G. puberulenta.

Gentiana lutea, great yellow gentian, native to Europe, is adventive in Alberta. Plants of this species are 0.5–2 m tall, with solitary, stout, unbranched stems and widely ovate to elliptic leaves to 30 cm. The flowers are borne in dense, terminal and axillary clusters and have bright yellow, deeply cleft corollas 10–25 mm, with five (to nine) spreading, linear lobes. As noted above, G. lutea lacks the plicae between the corolla lobes that are otherwise characteristic of the genus. Gentiana cruciata, crosswort or star gentian, also native to Europe, has escaped from cultivation in Manitoba and Massachusetts. It has a basal rosette of strap-shaped leaves, decumbent stems with numerous ovate-elliptic leaves, and flowers in small axillary and terminal clusters. The mostly four-lobed corollas are bright blue, 20–25 mm, with spreading lobes alternating with small, nearly symmetrically triangular or few-toothed plicae. Gentiana septemfida in the narrow sense, crested gentian or summer gentian, native to the Caucasus Mountains of Eurasia, has escaped in Ontario, Illinois, and Wisconsin. It resembles G. plurisetosa but has more numerous, lance-ovate leaves and usually more flowers per stem, in a terminal cluster. The corollas are deep blue, 30–50 mm, with spreading lobes and prominent, finely divided free portions of the plicae.

In addition to those mentioned above, some other European and Asiatic species of Gentiana are grown as ornamentals in North American gardens, although none has become really common in cultivation. Several species in sect. Ciminalis (Adanson) Dumortier and sect. Kudoa are cultivated in alpine gardens in the cooler parts of the flora area, and other species, mostly in sect. Cruciata and sect. Pneumonanthe, are cultivated in perennial borders.

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