Agriculture Reference
In-Depth Information
Tab l e 3 . 1
Chronology of crown nodes of selected groups of nodulated legumes. Data from Lavin et al.
(2005)
Major group
Mean age (Ma)
Standard deviation of mean
Leguminosae
59.0
0.2
Papilionodeae
58.6
0.2
Genistoids
56.4
0.2
Dalbergioids
55.3
0.5
Nodulated Caesalpinioideae
54.5
0.4
Swartzia
48.9
2.8
Mirbelioid
48.4
1.3
Robinioid
48.3
1.0
Millettioid
45.2
1.7
Mimosoideae
42.4
2.6
IRLC
39.0
3.2
Nodulated mimosoids (most)
33.2
3.2
Indigoferoid
30.0
3.3
Phaseoloid group
27.8
1.6
and included other fossils than those used by Lavin et al. (2005). As a result their time
span begins rather earlier, by about 5 million years. The Bruneau et al. (2008) paper
sheds considerable light on relationships within Caesalpinioideae, but, as the authors
hint, it does little to clarify the position with respect to origin of nodulation within this
group, except perhaps to support the idea of two or more nodulation events.
It is generally agreed that Mimosoideae is sister to Caesalpinioideae and evolved at a
later stage (Lavin et al., (2005). As discussed in Chapter 1, all the non-nodulating genera
(apart from some that may have lost this ability) are currently placed in tribeMimoseae,
although it is recognised that, until more data become available, this tribe is one of
convenience (Luckow, 2005). In Lavin et al. (2005), there are two branches from the
mimosoid crown node, dated at 42.4 Ma. One includes only the genus
Pentaclethra
,one
of the few genera that are known to have both nodulating and non-nodulating species
(Chapter 1). The other branch also has two parts, the first (and smallest) consisting of
eight genera, two of which (
Piptadeniastrum
and
Entada
) nodulate, one (
Pseudoprosopis
)
for which there is no information and with the rest (
Amblygonocarpus, Adenanthera,
Tetrapleura, Xylia, Calpocalyx
) appearing unable to nodulate (Sprent, 2001). Other non-
nodulating genera from tribe Mimoseae are not represented in the Lavin et al. (2005)
analysis. All the nodulating genera sampled, from all mimosoid tribes, are in a major
branch with a crown node dated at 33.2 Ma. The Bruneau et al. (2008) chronology is
similar to that of Lavin et al. (2005). Thus there appears to be a basal group of mimosoid
legumes that generally lack the ability to nodulate, as discussed in Sprent (2001). How
the occurrence of nodulation in Mimosoideae relates to that in Caesalpinioideae is
unclear. However, it is of interest and may be relevant, that in both sub-families, non-
nodulation is much more prevalent in Africa than in the Neotropics.
Parkia
is a genus
that once had its own tribe, but is now included in Mimoseae. It is the only genus in
the main nodulating section of Mimosoideae that appears not to nodulate, although
some species of
Acacia
may have lost this ability (Chapter 1).
