Angiosperms
Flowering Plants
Ecology & Form
Ancestral extant angiosperms (e.g. Amborella, Austrobaileyales, and Chloranthaceae) share ecophysiological traits associated with shady, disturbed, and wet habitats (Feild et al. 2004)
These features include low and easily light-saturated photosynthetic rates, leaf anatomy related to the capture of understory light, small seed size, and clonal reproduction
Some researchers have hypothesized that the earliest angiosperms were woody plants that grew in dimly lit, disturbed forest understory habitats and/or shady streamside settings
Evidence of the oldest known fossil angiosperms (e.g. Montsechia and Archaefructus) seems to indicate that flowering plants originated as herbaceous aquatic plants
Biology
Sporophyte (diploid) phase
Stems
Great variety of forms: herbs, vines, shrubs, trees
Xylem with vessel elements
Phloem cells with sieve elements
Stems exhibit a eustelic (eudicots) or atactostelic (monocots) pattern of vascular tissue
Maturation is usually endarch in stems
Leaves
Parallel or netted (reticulate) venation
Intercostal veins present, unlike most other living plant groups
These are veins in between larger veins that connect the smaller portions of leaf lamina
Roots
Roots exhibit a eustelic (monocots) or actinostelic (eudicots) pattern of vascular tissue
Maturation is usually exarch in roots
Reproductive structures
Flowers (determinate stem with modified leaves)
Carpal (megasporophyll) encloses ovules and become fruit after fertilization
Ovules that become seeds after fertilization
Double seed coat (integument) around ovule
Gametophyte (haploid) phase
Simple gametophyte; not free-living
Female ♀ gametophyte is reduced to 4-7 cells in ovule
no archegonium
Male ♂ gametophyte is just a few nuclei in pollen
Pollen wall morphology is columellar-tectate structure
Outer layer of the pollen wall (exine) is differentiated into two layers separated by columns
Geologic Range
Some controversial fossils indicate an Early or Middle Jurassic origin of angiosperms, including Euanthus, Nanjinganthus, Schmeissneria, Xingxueanthus, and Yuhania (Wang et al. 2007, Wang 2010, Wang & Wang 2010, Zheng & Wang 2010, Liu & Wang 2016, Liu & Wang 2017, Fu et al. 2018)
Molecular evidence seems to indicate an origin earlier than the Cretaceous (Coiro et al. 2019, Silvestro et al. 2021)
Classification
└Angiosperms
Angiosperms
├Amborellaceae
├Magnoliids
├Eudicots
├Ranunculales
├Rosids
├Caryophyllales
└Asterids
Diversity
Florigerminis jurassica †
late Middle Jurassic of the Daohugou Formation, Inner Mongolia, China
However, Wang et al. (2005) challenged the dating and claimed that the Daohugou Formation was of Early Cretaceous age
If the Jurassic age of the formation, and the analysis of the morphology of this fossil are correct, then Florigerminis is the earliest known flowering plant, although the Jurassic origin of angiosperms is disputed
Fossil includes not only a leafy, woody branch but also physically connected fruit and flower bud.
There is a flower bud located in-between a blooming flower and mature fruit
Leaves abscised, helically arranged, with decurrent petioles.
Flower–fruit pairs helically clustered on the distal portion of the branch.
Flower bud terminated on the branch, paired, with a straight pedicel, oval-shaped, with several tepals suggested by their sculpture.
Multiple tepals smooth-margined, tightly enwrapping the center.
Fruit born on a slender curving pedicel, oval-shaped, with four persistent decussately arranged foliar parts and an apical invagination.
Endocarp elongated oval, with a pointed tip.
Above: Figure 2, Cui et al. 2022 (a) Holotype of Florigerminis jurassica, showing the physically connected parts. Two (one missing to the left) fruits and a flower bud are on the branch terminal. Arrows point to the nodes on the branch. PB21737. The scale bar is 10 mm. (b) Close-up of the branch terminal showing a physical connection between two fruit pedicels (1 and 2) and a pedicel of flower bud (3). The scale bar is 2 mm. (c) Close-up of the fruit in (a). Note the mesocarp (m), endocarp (e), three persistent foliar parts visible (arrows), and connected pedicel (lower right). The scale bar is 2 mm. (d) Longitudinal fine striations on the branch surface. The scale bar is 0.25 mm. (e) The flower bud in (b). Note a foliar part at the bottom (arrow). The scale bar is 1 mm. (f ) Close-up of (e) showing overlapping distinct tepals (1–4). The scale bar is 0.2 mm. (g) Close-up of (e) showing distinct overlapping tepals in the top portion of the flower bud. The scale bar is 0.5 mm.
Dilcherifructus mexicana †
Middle Jurassic of Mexico
Possible fruit with an early origin for angiosperms
Fruit with depressions at both top and base, with a style in apical depression
Exocarpic epidermal cells polygonal or rectangular in shape, with straight cell walls
Stomata anomocytic, level with neighboring cells.
Single seed enclosed by a pericarp
Above: Dilcherifructus mexicana (Fig. 1, Wang 2021)
Montsechia vidalii †
Barremian from Spain (~130 Ma)
An early aquatic flowering plant which possessed no obvious flower parts, such as petals or nectar-producing structures for attracting insects
The fruit contains a single seed, which is borne upside down.
Montsechia is possibly related to the living Ceratophyllum
This fossil is the earliest definitive evidence of angiosperm fossil leaves and flowers
Above: Montsechia vidalii
Right: Montsechia vidalii bearing fruits (Fig. 8, Gomez et al. 2015)
Archaefructus †
Barremian (~124.6 Ma)
One of the earliest known genera of flowering plants
Herbaceous and aquatic plant
carpels and stamens, sometimes produced on elongate stem
Staminate (male) flowers proximal and pistillate (female) flowers distal
Archaefructus may not be basal within angiosperms, but close to the Nymphaeales or the basal eudicots.
A. eoflora †
Barremian from Beipiao, Western Liaoning, China
Unlike other species, A. eoflora lacks an extended section of male flowers
Male flowers are located closely proximal to carpellate flowers
A. liaoningensis †
Barremian from the Yixian Formation, Liaoning, China
A. sinensis †
Barremian from the Yixian Formation, Liaoning, China
Above: Archaefructus liaoningensis
Additional Resources
Flowers may be more ancient than dinosaurs – but scientists can’t agree on when they evolved (The Conversation 9Apr2024)
└Silvestro et al. (2021) Fossil data support a pre-Cretaceous origin of flowering plants
The earliest angiosperm is a eudicot? (Paleobotany Blog 1Dec2013)
The Prehistoric Path to Flowering Plants (In Defense of Plants 6Jun2021)