New insight into the morphology of the long shoots of Pinus (Pinaceae)

Previously used morphological classifications of the long shoots of the genus Pinus were found to be insufficient to describe the various forms existing among all species and their fluctuation. Along with the uninodal shoot form, the multinodal form (sometimes differentiated into perfect or imperfect) has been distinguished for more than one hundred years. However, the latter term was found to comprise several neglected but conspicuously different growth forms across the global species diversity of this genus. The primary objective of this research was to reassess all growth forms of the long shoots of pines based on field investigation on more than 100 species. A new classification system of vigorous, annual, fertile long shoots of pines is proposed. The original term uninodal is retained, whereas the content of the ambiguous and here excluded term “multinodal” is divided into six specific morphotypes, which represent different developmental forms of more than one node per year. These are newly designated as addinodal, laterinodal, cryptonodal, seronodal, gradinodal and plurinodal, and each morphotype is illustrated with typical examples. The fluctuation and imperfect forms of morphotypes within a species or individual and the juvenile forms of the long shoots are commented. A conclusion table specifying the occurrence of fertile shoot morphotypes in all species of Pinus and juvenile shoot forms in the majority of species is provided. Particular fertile shoot morphotypes occur in the genus Pinus very unevenly: the uninodal morphotype was found in 63 species, the addinodal in 58 species, the plurinodal in 22 species, the seronodal in 10 species, the laterinodal in 8 species, the gradinodal in 7 species, and the cryptonodal morphotype was found in 2 species. Except for the last morphotype, which is found only in America, the others occur in species of Eurasia and America.