Dear Sid Ji, Theory that I have put forward is simply my personal knowledge about paleobiology, as I don’t have fossil records in my hand hence I have used the word speculative. It is really wonderful to know that prominent evolution biologists support the idea. Even many India famous Biologists think my knowledge in Botany is also speculative (in negative sense), hence you see speculation is term quite long standing for me.
Analyses of the plastid *rbcL* gene played an early role in our evolving understanding of legume phylogeny. Results from studies by two groups (e.g., Käss and Wink, 1996, 1997; Doyle et al., 1997) were largely concordant with earlier work, confirming for example the monophyly of smaller groups suggested by other molecular evidence (e.g., Lavin et al., 1990; Sanderson and Wojciechowski, 1996) or morphology (Chappill, 1995), and the monophyly of the traditional subfamilies Mimosoideae (“mimosoids”) and Papilionoideae (“papilionoids”), nested within a paraphyletic Caesalpinioideae (“caesalpinioids”). Many of these groups have received additional support and have been more clearly resolved by subsequent, more extensive studies using the plastid *trnL* intron, alone or in combination with morphology (e.g., Bruneau et al., 2001; Pennington et al., 2001; Herendeen et al., 2003), the plastid *matK* gene and flanking *trnK* intron (e.g., Hu et al., 2000; Luckow et al., 2003; Wojciechowski et al., 2004), the nuclear ribosomal DNA ITS region (e.g., Sanderson and Wojciechowski, 1996; Allan and Porter, 2000), or a combination of these and other molecular loci (Lavin et al., 2001, 2003). The fossil record of the Fabaceae is abundant and diverse, particularly in the Tertiary, with fossil flowers, fruits, leaflets, wood, and pollen known from numerous localities; some examples are shown in the figures below (Crepet and Taylor, 1985, 1986; Crepet and Herendeen, 1992; Herendeen, 1992; Herendeen et al., 1992). Although there are several reports of earlier fossils, *Sindora*-like pollen (subf. Caesalpinioideae) from the Maastrichtian of Canada, Columbia, and Siberia (Raven and Polhill, 1981) and woods similar to *Cassia* s. l. and Mimosoideae from the same time period (e.g., Müller-Stoll and Mädel, 1967), they cannot be assigned unequivocally to legumes. The first definitive legumes appear during the Late Paleocene (ca. 56 Mya; Herendeen, 2001; Herendeen and Wing, 2001; Wing et al. 2004). Representatives of all three traditionally recognized subfamilies, the caesalpinioids, mimosoids, and papilionoids (Polhill et al., 1981), as well as other taxonomically large clades within these subfamilies (e.g., “genistoids”), are recorded from the fossil record soon afterward, beginning around 50 to 55 Mya (e.g., Herendeen et al., 1992). Indeed, the occurrence of diverse assemblages of taxa representing all three subfamilies at multiple localities dating from the middle to upper Eocene, especially the Mississippi Embayment of southeastern North America, suggests that most major lineages of woody legumes (except for the tribe Cercideae) were present and extensive diversification had taken place by this time (Herendeen et al., 1992). Attempts to estimate the age of legumes and diversification in the family, based on molecular sequence data, have been published in recent years. Wikström et al. (2001) used a non-molecular clock based analysis of the three gene data set (plastid *atpB* & *rbcL*, and nuclear 18S rDNA genes; Soltis et al., 2000) with a minimum age of 84 Ma for the split between Fagales and Cucurbitales as an internal calibration point, and estimated an age for Fabaceae of 74-79 Ma. A comprehensive analysis of rates of molecular evolution and estimated ages for crown groups within the legume family has been presented by Lavin et al. (2005). In this study, Tertiary macrofossils that showed distinctive combinations of apomorphic characters or features were used to constrain the minimum age of 12 specific internal nodes to estimate ages of a number of the clades identified in recent family-wide phylogenetic analyses of plastid *matK* (Wojciechowski et al., 2004) and * rbcL* (Kajita et al., 2001) gene sequence data. Their findings indicate the age of the legume crown clade differs by only 1.0 to 2.5 Ma from the age of the stem clade and the oldest caesalpinioid, mimosoid, and papilionoid crown clades show approximately the same age range of 40 to 59 Ma, findings consistent with a rapid diversification of the family soon after its origin during the Late Paleocene. Remarkably, three large clades that include papilionoids traditionally considered derived (Polhill et al., 1981; Polhill, 1994), the “dalbergioids” (Lavin et al., 2001), “Hologalegina” (Wojciechowski et al., 2000), and “mirbelioids” (Crisp et al., 2000), all have ages estimates in the 50-Ma time frame or older. One of these, Hologalegina, contains many of the well-known temperate, herbaceous species of legumes grown as food and forage crops (e.g., alfalfa, clovers, peas, and lentils). Adopted: Tree of Life Web Project [http://tolweb.org/Fabaceae/21093] Tanay On Thu, Jul 29, 2010 at 5:12 PM, Pankaj Kumar <[email protected]>wrote: > Dear Sid, > Thanks a lot for the clarification. I can make out that you have a > good hold on understanding the studies on Molecular systematics. I > would really be interested in knowing about your whereabouts to learn > more from you as I dont know much abt this field and hence I would be > interested in getting in touch with u. My email id is > [email protected]. > At the same time I really like Tanay's comments on, "If Heterostemon > from upper Amazon has similarity then there should me some evidences > in middle and lower Amazon in form of fossils for T indica, or any > kind of transitional plant". My confusion was based on Heterostemon's > origin in amazon...but lets see as said by him this theory is > speculative and not affirmative and as said by you that it is > possible. > Lets say, may be due to inadequate sampling we cant reach to conclusion. > Thanks again for putting up so much of info on a simple Tamarind!!!! > This shows we still need to study hard each and every plant in our > locality to understand every aspect of it. > > Nice....keep it up.... > Regards > Pankaj > -- Tanay Bose +91(033) 25550676 (Resi) 9830439691(Mobile)
