MOLECULAR PHYLOGENY OF PINACEAE AND PINUS

Abstract

Molecular phylogenetic reconstructions of Pinaceae based on immunological approaches plus nuclear and organellar DNA sequences consistently resolve the generic pairs Larix – Pseudotsuga and Abies – Keteleeria. In most analyses Pseudolarix and Tsuga (including Nothotsuga) form a clade that is sister to the Abies Keteleeria clade, and Cathaya, Picea, and Pinus make up an unresolved trichotomy. The position of Cedrus remains problematic; molecular evidence supports a basal position in the family. Within Pinaceae genera, molecular phylogenetic reconstructions have markedly improved our understanding of species relationships and biogeography in Pinus, Larix, Pseudotsuga, and Tsuga. Molecular phylogenetic approaches have become routine in plant systematics, and many researchers have applied these methods in conifers. This paper reviews molecular phylogenetic studies of Pinaceae and its constituent genera, with a focus on Pinus, the largest genus in the family. PINACEAE Pinaceae comprises eleven recognized genera and 225 species (Table 1), making it the largest family of non-flowering seed plants. Pinaceae often form the dominant component of boreal, coastal, and montane forests over large regions of the Northern Hemisphere, and several species are now widely planted for reforestation and wood production in both hemispheres. Thus the family has tremendous ecological and economic importance throughout the temperate and in many subtropical regions of the world. There is considerable morphological and molecular evidence for the monophyly of Pinaceae. Hart’s (1987) morphological cladistic analysis of all conifer genera recorded ten synapomorphies, including ovulate cone scales distinct from subtending bracts, two inverted ovules per scale, and a terminal seed wing. Additional synapomorphies come from embryology, chemistry, and phloem characters (see Price, 1989 for details), rbcL (Chase et al. 1993), and nuclear 18S rRNA (Chaw et al. 1997) sequences. Price (1989) reviewed the history of Pinaceae subfamilial classification. He concluded that either two subfamilies (Table 1) or three subfamilies (Abietoideae, Laricoideae and a monogeneric Pinoideae) were “reasonable alternatives.” Frankis (1989) recognized four subfamilies: Abietoideae, Laricoideae (containing Cathaya, Larix and Pseudotsuga) and monogeneric Piceoideae and Pinoideae. We prefer a more broadly circumscribed Pinoideae (Table 1). Proc 4 IS on Conifer