Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 7, 14

Schmeissneria: A Missing Link to Angiosperms?

Affiliations

Schmeissneria: A Missing Link to Angiosperms?

Xin Wang et al. BMC Evol Biol.

Abstract

Background: The origin of angiosperms has been under debate since the time of Darwin. While there has been much speculation in past decades about pre-Cretaceous angiosperms, including Archaefructus, these reports are controversial. The earliest reliable fossil record of angiosperms remains restricted to the Cretaceous, even though recent molecular phylogenetic studies suggest an origin for angiosperms much earlier than the current fossil record.

Results: In this paper, after careful SEM and light microscopic work, we report fossils with angiospermous traits of the Jurassic age. The fossils were collected from the Haifanggou Formation (middle Jurassic) in western Liaoning, northeast China. They include two female structures and an associated leaf on the same slab. One of the female structures is physically connected to the apex of a short shoot. The female organs are borne in pairs on short peduncles that are arranged along the axis of the female structure. Each of the female organs has a central unit that is surrounded by an envelope with characteristic longitudinal ribs. Each central unit has two locules completely separated by a vertical septum. The apex of the central unit is completely closed. The general morphology places these fossils into the scope of Schmeissneria, an early Jurassic genus that was previously attributed to Ginkgoales.

Conclusion: Because the closed carpel is a character only found in angiosperms, the closed apex of the central unit suggests the presence of angiospermy in Schmeissneria. This angiospermous trait implies either a Jurassic angiosperm or a new seed plant group parallel to angiosperms and other known seed plants. As an angiosperm, the Liassic age (earliest Jurassic) of Schmeissneria microstachys would suggest an origin of angiosperms during the Triassic. Although still uncertain, this could have a great impact on our perspective of the history, diversity and systematics of seed plants and angiosperms.

Figures

Figure 1
Figure 1
A general view of female structures, leaf, and short shoot. a. A general view of two female structures (a, b) and one leaf (c) on the same slab. The specimen A is the holotype, and specimens B and C are the paratypes. Specimen numbers 8604a, 8604b, and 8604c. Bar = 2 cm. b. A detailed view of specimen B in Fig. 1a. Note the twisted axis of the female structure and the attached female organs. Specimen number 8604b. Bar = 1 cm. c. A detailed view of the short shoot. Note the leaf cushion (black arrow) and the axis of the connected female structure (white arrow). Specimen number 8604a. Bar = 2 mm.
Figure 2
Figure 2
The morphology and structures of the female organs. a. Several female organs attached to the axis of the female structure (A). Note the longitudinal ribs on the sheathing envelope and the central unit (O), the short peduncle (arrow), the extended envelope apex, and dark coaly residues. Specimen number 8604a. Bar = 3 mm. b. Several female organs attached to the axis of the female structure (A). Note the envelope (P) and central unit (O), the fused bases of the female organ pair (white arrow), the mark on the central unit left by the fallen envelope (black arrow), and the extended envelope apex. Specimen number 8604a. Bar = 3 mm. c. An isolated female organ pair in the proximal portion of specimen A. Only one of the pair is evident (white arrow); the other one (black arrow) is obscure due to preservation. Note the longitudinal ribs on the axis of the female structure (A) and the less-extended envelope apex. Specimen number 8604a. Bar = 1 mm. d. The top female organ pair in specimen B. Note the longitudinal ribs on the sheathing envelope, the relic of the missing female organ of the pair (arrow), and the less-extended envelope apex. Specimen number 8604b. Bar = 1 mm. e. A female organ pair in the proximal portion of specimen A. Note the axis of the female structure (A), central units (O), sheathing envelope (P), fused female organ bases (arrow), their spatial relationship (the axis of the female structure is in the foreground), and the extended envelope apices. Colored from an original greyscale picture. Refer to Fig. 4a. Specimen number 8604a. Bar = 2 mm. f. Female organs attached to the axis of the female structure. Note the longitudinal ribs on the axis of the female structure (A), female organs of various sizes and orientations, longitudinal ribs on the envelope, and the extended envelope apex. Specimen number 8604a. Bar = 2 mm. g. A detailed view of the rectangular region in Fig. 2f. Note the exposed internal details of the central unit, smooth wall in the lower part, rough wall in the upper part, large locule, and dark coaly residue. Because the septum and part of the central unit are raised above the level of the side wall, they cast a dark shadow on the latter (arrow) and the shadow extends from the base to the upper parts of the central unit. Refer to Fig. 4b. Specimen number 8604a. Bar = 1 mm. h. A view of a female organ with the exposed interior details of the central unit with the SEM. Note the central unit margin (black arrow) and papillate septum (white arrow and upper left inset) distinct from the interior wall with longitudinal ribs. Specimen number 8604a. Inset bar = 20 μm, Bar = 0.5 mm.
Figure 3
Figure 3
Detailed views of the internal structure of female organs. a. A female organ with a broken envelope and its exposed central unit. Note the sheathing envelope (P), central unit (O), and longitudinal ribs with dark coaly residues on them. The central unit is attached to the receptacle by a wide base (arrow). Specimen number 8604a. Bar = 1 mm. b. A view of the envelope apex of the female organ in Fig. 3d with the SEM. Note the elongated cells on the smooth epidermis and slightly elongated cells in the tissue of the envelope (arrows). Specimen number 8604b. Bar = 0.1 mm. c. A view of an envelope fragment with the SEM. Note the smooth surfaces and the border between different parts of the envelope (arrow). Specimen number 8604a. Bar = 50 μm. d. A view of a female organ with the envelope (P) and the central unit (O) with the SEM. The texture and the central unit outline (white arrow) could be traced to the envelope apex (black arrow). On the right, there is another female organ with its apex plunging into the sediment matrix (black rectangle). Specimen number 8604b. Bar = 0.5 mm. e. A detailed view of the rectangular region in Fig. 3d with the SEM. Note the spatial relationship between the envelope (P) and the central unit (O), and the longitudinal ribs (arrow) on the internal walls of the central unit. Specimen number 8604b. Bar = 0.1 mm. f. A detailed view of the apex of the central unit in Fig. 3e (rectangle) with the SEM. Note the septum (arrow) across the central unit (O) apex. The black dot beside the bar is about 20 μm in diameter, the size of an average pollen grain. An entry point for a pollen grain of similar size, if present, would be hard to ignore in this image. Therefore, at least the tip of the upper locule (carpel), which is not eclipsed by the septum vestige or in its shadow, is closed. Specimen number 8604b. Bar = 0.1 mm. g. A cross section of two female organs embedded in the sediment. Note the pale sediment (upper half), dark resin (lower half), and darker stripes of two fused female organs (a and b, outlined by black and white lines, respectively). Specimen number 8604a. Bar = 0.5 mm. h. A detailed view of the female organ in Fig. 3g. Note the septum (arrow) and its smooth connection to the side walls of the central unit. Specimen number 8604a. Bar = 0.1 mm. i. A thin section across the apex of the central unit in Fig. 3f. Note the septum (arrow) separating two locules and its smooth connection to the side walls. Light microscope. Specimen number 8604b. Bar = 0.1 mm. j. A view of the internal surface of an envelope apex with the SEM. Note the converging longitudinal ribs. Specimen number 8604a. Bar = 0.5 mm. k. A detailed view of the rectangular region in Fig. 3j. Note the pollen grain (arrow) adherent to one of the longitudinal ribs on the internal surface of the envelope. Specimen number 8604a. Bar = 50 μm. l. A detailed view of the pollen grain in Fig. 3k. Specimen number 8604a. Bar = 10 μm. m. The rugulate sculpture on the pollen grain in Fig. 3l. Specimen number 8604a. Bar = 2 μm. n. Another pollen grain adherent to the internal surface of the envelope apex. Specimen number 8604a. Bar = 5 μm. o. The rugulate sculpture on the pollen grain in Fig. 3n. Specimen number 8604a. Bar = 2 μm.
Figure 4
Figure 4
Diagrams of the female organs and the reconstructions of S. sinensis. a. Schematic diagram of the female organ pair shown in Fig. 2e. Note the female organs' fused bases (a), the central unit (b), the sheathing envelope (c), and the axis of the female structure (d). b. Schematic diagram of the female organ in Fig. 2g. Note the smooth locule walls (a and c, probably due to the fallen ovules) and the rough internal walls (g) on each side of the septum (b), different parts of the envelope (d and f), the relic of the broken central unit (e), the vertical septum (b) connected to the base of the central unit. c. A reconstruction of a female organ of S. sinensis. Note the short peduncle of the female organ pair (a) connected to the axis of the female structure (for simplicity, only one organ of the female organ pair is shown here), the central unit (b), two locules (c), the septum (d) separating the two locules, and the sheathing envelope (e). d. Schematic diagram of S. sinensis. From the bottom, note the apex of the short shoot, axis of the female structure, isolated immature female organ pair, clustered female organ pairs along the axis of the female structure, and terminal female organ pair.
Figure 5
Figure 5
The geographic position of the type fossil locality of S. sinensis. The upper right inset shows northeast China, and the black area within is Liaoning Province. The rectangular area in the inset is shown in detail in the main map. The black dots are the major cities in the region, and the black triangle is the type locality of S. sinensis, Sanjiaochengcun, Jinxi, Liaoning, China (120°21'E, 40°58'N).

Similar articles

See all similar articles

Cited by 6 PubMed Central articles

See all "Cited by" articles

References

    1. Eames AJ. Morphology of the angiosperms. New York: McGraw-Hill Book Company; 1961.
    1. Heywood VH. Flowering plants of the world. Oxford: Oxford University Press; 1979.
    1. Friis EM, Chaloner WG, Crane PR. Introduction to angiosperms. In: Friis EM, Chaloner WG, Crane PR, editor. Origins of angiosperms and their biological consequences. Cambridge: Cambridge University Press; 1987. pp. 1–15.
    1. Cronquist A. The evolution and classification of flowering plants. Bronx: New York Botanical Garden; 1988.
    1. Hughes NF. The enigma of angiosperm origins. Cambridge: Cambridge University Press; 1994.

Publication types

LinkOut - more resources

Feedback