Early angiosperms from the Lower Cretaceous of Jixi, eastern ...

only from dispersed pollen grains.It is signi¢cant
that we have the same pollen type from an in£orescence
in situ which is seemingly attached to a
dicotyledonous leaf.Previously it was thought
that the sulcus of monosulcate angiosperm pollen
were derived from a gymnosperm ancestor which
had monosulcate pollen.However, Brenner proposes
a new model for the evolution of the monosulcate
aperture in angiosperms.He suggests that
the sulcus was developed from within the angiosperm
lineage and that its presence in angiosperms
is entirely an angiosperm feature and not
derived from a non-angiospermous ancestor.The
inaperturate nature of both the pollen mention
here and that described by Brenner may be the
result of the sometimes cryptic nature of apertures
in some angiosperms. Endress (1987) indicates
that in some genera the apertures are often hidden
by reticulate exine ornamentation.The occurrence
of very similar, small, circular, ‘inaperturate’, reticular,
tectate-columellate pollen which Brenner
found as dispersed pollen in Israel, is known
from a megafossil in situ in China.This new material
may provide new characters useful in understanding
the nature of early angiosperms.
The in£orescence consists of a clustering of
small helically arranged £orets borne on a rather
stout axis.Because of the carbonaceous nature of
the preservation and the crowded nature of the
£orets, it is di⁄cult to discern the nature of
each £oret.The parts seem to be very small, forming
£orets 1.0^1.5 mm in diameter. Since the pollen
are derived from the £orets in situ, we assume
that there were anthers in the £orets, but do not
know if the £orets were bisexual or unisexual.
However, it seems most probable that since the
reproductive axis appears to be still attached to
the leaf, in which axis it was borne, and because
Plate V.
G. Sun, D.L. Dilcher / Review of Palaeobotany and Palynology 121 (2002) 91^112 107
most all of the £orets are still attached to a common
axis, with no indication of fruit formation,
that the £orets are young or immature.Because
pollen is present and well formed, perhaps the
pollen bearing organs matured before the ovules.
Nevertheless, until we can collect additional material
and make more preparations, we consider
that these £orets were either bisexual or male.
Small bisexual £orets have been described from
the Albian (Friis et al., 1994) and Turonian (Crepet
and Nixon, 1994) sediments in eastern North
America.These £orets are small (2.2 mm), pedicellate,
bear monosulcate pollen and are described
as isolated £orets.The only feature similar between
the fossil £orets of Virginianthus and Xingxueina
is the small size of the £orets.But this is
important because it indicates that several early
angiosperms had £owers that were small, many
of which were crowded upon an individual axis.
Friis et al.(1994) compares Virginianthus with
Calycanthaceae and notes many similarities between
the fossil and several genera of that family,
several of which have small £orets. Crepet and
Nixon (1994) in their review of the fossil £owers
of the Magnoliidae suggest that the angiosperm
ancestral groups probably had small simple £owers
with parts in whorls similar to that known for
the Chloranthaceae, Platanaceae, Buxaceae and
Lauraceae (Friis et al., 1991).Also, Dilcher
(1979) suggested that early angiosperms may
have had small simple £owers.The reproductive
axis appears to be borne in the axil of the leaf of
Xingxuephyllum (Plate V, 1B, Fig.4G).There are
two small carbon fragments of the petiole missing,
but it appears as if the petiole continued to the
slightly enlarged base which is in common with
the base of the reproductive axis.We also considered
a possibility that the two fossils just hap-
1A, 3^5. Xingxueina heilongjiangensis Sun et Dilcher.
1A, 3. In£orescence, SC10025. 1A. Bar = 0.5 cm. 3. Bar = 0.2 cm.
4.Pollen grain from the in£orescence.SEM0775.Bar = 10 Wm.
5.Pollen grains in situ on the surface of the in£orescence as viewed by epi£uorescence microscopy, SC10025.Bar = 80
Wm.
1B, 2. Xingxuephyllum jixiense gen.et sp.nov.Incomplete leaf probably connected organically with the in£orescence,
Holotype SC10026. 1B. Bar = 0.5 cm. 2. Bar = 0.6 cm.