Sargent, Charles S. 1889. Vaccinium hirsutum. Gard. & Forest. 2: 364, 365, fig. 119.
Ericaceae
Species Description - Plants usually in compact colonies (10)15-35 centimeters high. (The twigs of the current season markedly glaucous.) Leaves deciduous, glaucous on both surfaces; the lower surface non-glandular and glabrous; elliptic, often acuminate, 1-1.5 cm. wide, 1.5-4 cm. long; the margin sharply serrate. Corolla cylindro- campanulate, 5-6 mm. long, white or whitish. Fruit dark, sometimes shining black or rarely dull and subglaucous, 8-12 mm. in diam., of excellent flavor.
Vaccinium nigrum Britton, Mani. 710. 1901. Not V. nigrum Steud. Nom. Bot. (Phanerog.) ed. 1. 867. 1821. (Erroneously attributed to Desfontainies.) Not V. nigrutm (Wood) Britton, Mem. Torrey Club 5: 252. 1894.
Tetraploid (2n = 48).
V. brittonii not only appears to occupy much the same general range as V. tamarckii, but is also homoploid; for theseireasons there might be some doubts concerning the wisdom of considering it a separate species. However, there is rarely any trouble in distinguishing them in the field, and herbarium material seldom causes confusion if carefully examined. Certainly they should be nomen- claturally distinguished in some way, and since there is so little chance of error they are here treated as separate species pending the accumulation of the perti- nent data needed to unite them under the same binomial with any degree of confidence.
Among the items which future study should determine is the relative propor- tion of brittonii and lamarckii plants in different regions; this will require careful surveys and large series of mass collections, as well as an analysis of the ecologi- cal requirements of this homoploid pair. Although it is fairly susceptible to burning-so that it is usually excluded from the commercial fields-preliminary observations in a few relatively undisturbed areas gave some indication that V. brittonii tends to favor the same habitat as V. angustifolium, which may possibly explain why hybrids between brittonii and lamarckii are not more abundant. Also it will be valuable for a possible reinterpretation of this material when once a complete cytogenetical analysis of these two species is done. Apparently something has happened which is unusual for the group of blueberry species. With the exception of V. myrtilloides, aimgustifolium, lamarckii, and brittonii, there is a reasonably close correlation in the amount of glauceseence on the epidermis of the leaves; twigs, and fruit.34 This is not a casual observation, but has held in so many thousands of plants, both in the wild and in the trial plots where the artificially produced hybrids are tested, that I feel reasonably safe in making it a generalization-that is, except where material in some way involving the four species mentioned is concerned, as in hybrids between lamarckii and brittonii, and between either of these and other tetraploids, such as corymbosum. The same applies to the hybrids with myrtilloides.
There is no need to speculate in this place on the possible cytological phe- nomena attending the evolution of these forms, but a complete analysis of the situation would go far toward solving the manner of development of the poly- ploid species in this series. V. brittonii may be a mutant derived from V. lamarckii, or it may be a polyploid derived from a mutant form of angustifoliurm. In discussing these items, it should be pointed out, since brittonii is of no great commercial importance, that we have not pressed the accumulation of material of it as with other species. As a result, I am by no means satisfied with these con- eluisions; further work may demonstrate (just as it has for augustifolittn vs. lamarckii) that diploids and tetraploids are both present. However, taken as a whole, the material of V. brittonji appears to be more homogeneous than that of the combined populations of angustifolium and lamarckii, tending to be a closer parallel with the tetraploid latmarckii than with the diploid angustifolium.
Hybrids between brittonii and lamarckii are known. Where these have been found, one of . the apparently commoner types of segregates is that with the green, shining leaves characteristic of lamarckii, and the dark fruit of brittonii. This segregate form was described under the name of V. pennsylvanicum var. nigrum Wood; it is reasonably common in those areas where Professor Wood is known to have carried on much of his field observation. Hybrids between brittonii and corymbosum are also known, but appear to be rather rare.
Another described plant, Vaccinium fissum Schranck, has been placed in synonymy under V. angustifolium in spite of the fact that its berries were said to be black. The type (in Herb. Monac.) has not been examined in this study, nor is the photograph conclusive. The leaves appear to be a much closer match for those of V. angustifolium than for those of V. brittonii; furthermore, if described from the dried material, the note on fruit color would be quite unreliable, for the glauceseence of the fruit of angustifollium may be easily lost during pressing. Furthermore, Schranck's specimen appears to have been collected in Labrador where brittonii. is unknown; whereas acngustifolium is at least locally common there.
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