Rhodora: JOURNAL OF THE NEW ENGLAND BOTANICAL CLUB 45(533): 169-170 (May 1943)
THE PROBABLE RELATIONSHIP OF PHASEOLUS POLYSTACHIOS TO OTHER SPECIES
H. A. ALLARD

THE only wild native bean in the eastern United States is the so-called Kidney Bean, Phaseolus polystachios (L.) BSP. This bean inhabits the Coastal Plain and the Piedmont areas, but is not found in high-mountain areas. It is a rather rare species of rich deciduous woods, where its perennial root can find winter protection under thick blankets of ground-debris and decaying leafage.

While the name "Kidney Bean" would suggest that it belongs to the species-assemblage represented by P. vulgaris L., there is reason to believe that its affinities may be nearer the assemblage of the Scarlet Runner beans represented by the species P. coccineus L. This conclusion is based upon the following behaviors.

The cotyledons of the P. coccineus assemblage and also of P. polystachios are hypogean, remaining buried in the soil, as in the case of Pisum. So far as known no members of the species P. vulgaris have this habit, the cotyledons always being carried above the soil at germination.

With respect to their length-of-day responses the varieties of P. coccineus tested by the writer and by other workers, have shown strong tendencies to flower most freely when experiencing long days. These varieties have either failed to flower or flowering has been greatly reduced when given daily photoperiods of 10 hours. If flowers developed, these were usually sterile or fruited very late in the season.

1 Complete or Partial Inhibition of Flowering in Certain Plants when Days are too Short or too Long. H. A. Allard, Jour. Agr. Res.. 57 (10), 1938.

It may be stated that the Wild Bean, P. polystachios, becomes a dwarf, bushy, completely flowerless plant when given 10 hours of light. The writer's studies1 have shown that it is an intermediate plant in its length-of-day behavior since flowering occurs only within a definite range of lengths of day. At certain lower limits flowering ceases because the days are too short, and at certain upper limits flowering ceases or is less profuse because the days are too long. P. polystachios is definitely not a short-day type and flowering is favored by long days which do not exceed certain limits. There are, on the other hand, few if any of the varieties of the P. vulgaris assemblage which show long-day tendencies or find lengths of day of 10 or 12 hours unfavorable to flowering.

2 Further studies in Photoperiodism, the response of the plant to relative length of day and night, W. W. Garner and H. A. Allard, Jour. Agr. Res. 23, 1923.
    Effect of length of day on flowering and growth. M. A. H. Tincker. Nature, Sept. 6, 1924. p. 330.
    Further observations on the responses of various species of plants to length of day. H. A. Allard and W. W. Garner. U. S. Dept. of Agr. Tech. Bull. 727. 1940.

In response to short photoperiods the roots of varieties of P. coccineus have usually shown strong tuberization and P. polystachyios has shown similar tendencies, both in the field and when long-day conditions favorable to flowering have been denied the plants.2

Both P. polystachios and P. coccineus show a greater degree of hardiness than members of the P. vulgaris assemblage. In England the Scarlet Runner beans sometimes overwinter by means of their tuberous roots, and for the same reason, the Wild Bean of eastern North America has become a perennial species.

These similarities of behaviors and responses that characterize the Wild Bean and the Scarlet Runner assemblage, more especially the hypogean behavior of the cotyledons, would indicate the former is more closely allied with the P. coccineus assemblage than to the kidney beans, P. vulgaris.

WASHINGTON, D. C.