divided into two subgenera based on the number of fibrovascular bundles in the needle. The subgenera can be distinguished by cone, seed, and leaf characters: Pinus subg. Pinus, the yellow, or hard pine group, generally with harder wood and two or three needles per fascicle. The subgenus is also named diploxylon, on account of its two fibrovascular bundles. Pinus subg. Strobus, the white, or soft pine group. Its members usually have softer wood and five needles per fascicle. The subgenus is also named haploxylon, on account of its one fibrovascular bundle. Phylogenetic evidence indicates that both subgenera have a very ancient divergence from one another. Each subgenus is further divided into sections and subsections. Many of the smaller groups of Pinus are composed of closely related species with recent divergence and history of hybridization. This results in low morphological and genetic differences. This, coupled with low sampling and underdeveloped genetic techniques, has made taxonomy difficult to determine. Recent research using large genetic datasets has clarified these relationships into the groupings we recognize today. Etymology The modern English name "pine" derives from Latin pinus, which some have traced to the Indo-European base *pīt- ‘resin’ (source of English pituitary). Before the 19th century, pines were often referred to as firs (from Old Norse fura, by way of Middle English firre). In some European languages, Germanic cognates of the Old Norse name are still in use for pines — in Danish fyr, in Norwegian fura/fure/furu, Swedish fura/furu, Dutch vuren, and German Föhre — but in modern English, fir is now restricted to fir (Abies) and Douglas-fir (Pseudotsuga). Phylogeny Pinus is the largest genus of the Pinaceae, the pine family, which first appeared in the Jurassic period. Based on recent Transcriptome analysis, Pinus is most closely related to the genus Cathaya, which in turn is closely related to spruces. These genera, with firs and larches, form the pinoid clade of the Pinaceae. Pines first appeared during the Early Cretaceous, with the oldest verified fossil of the genus is Pinus yorkshirensis from the Hauterivian-Barremian boundary (131–129 million years ago) from the Speeton Clay, England. The evolutionary history of the genus Pinus has been complicated by hybridization. Pines are prone to inter-specific breeding. Wind pollination, long life spans, overlapping generations, large population size, and weak reproductive isolation make breeding across species more likely. As the pines have diversified, gene transfer between different species has created a