Spontaneous white pine hybrids

With two platesA NOTEWORTHY FEATURE of the genus Pinus L. is the relative abundance of both natural and artificial hybrids.Summaries of known crosses published in recent years include hybrids within both of the subgenera Haploxylon Koehne and Diploxylon Koehne, usually within the series limits of these subgenera; cf.L. P. V. Johnson (3), Richens (5), Righter and Duffield (6).The hybrids to be described here are hitherto unreported in the subgenus Haploxylon.In the spring of 1949 a five-needled pine growing in the Hunnewell Arboretum, Wellesley, Massachusetts, was observed to differ markedly from the familiar native white pine, Pinus strobus L.; and yet it was evidently not one of the known cultivated species of this group of pines.The tree, about twenty years old, twenty-five feet high, and fourteen inches d. b. h., is, in the opinion of Mr. Walter Hunnewell, of spontaneous origin, inasmuch as he has no record nor recollection of it having been planted.Apparently it is a chance seedling which has grown up since annual mowing was discontinued in the Arboretum about 1930.It has been allowed to remain because of its unusually attractive blue-green foliage.The tree is a vigorous and rank grower of loose open habit.This rapid growth capacity plus the effect of repeated weevil damage has caused it to develop a broad crown with several leaders.Although generally resembling our native white pine it differs in the curved and twisted blue-green foliage, the more massive cones, the larger, purple-brown seeds, and the scaly brown bark.The flowers at the time of initial observation were seen to differ from those of white pine in both position and color.The red female flowers were borne from top to bottom of the tree, while on white pine they rarely are found except in the topmost branches.The flesh-colored male flowers were few and borne in elongated clusters instead of in yellow compact bunches as in white pine.Subsequent examination of the pollen showed it to be 23% defective.The presence in the Arboretum of P. parviflora Sieb.& Zucc.and of P. parviflora var.pentaphylla Henry, both of which have flowering habits similar to the tree in question, suggested the possibility of hybridization with the native white pine, which is abundant on the grounds.Since the difference between P. parviflora and its variety pentaphylla is slight and of such a nature as to be obscured in a hybrid, the latter taxon is not being considered as distinct for the purposes of this paper.Moreover, the location of this varietal form in respect to the other trees in the Arboretum substantially reduces the probability of it having had a rdle in the induction of this presumed hybrid or of others discovered later.