Angiosperms represent a monophyletic group

• Vessels present in xylem (shared with gnetophytes)
• Ovules in bisexual strobili (flowers)
• Ovules enclosed by carpels
• Endosperm present (resulting from double fertilization, which also occurs in gnetophytes)

Origin of Angiosperms

• Late Jurassic/early Cretaceous (140 MYBP)
• Evolved from gymnosperms (share seed characteristic)
• Identity of ancestor is unknown
• Sister lineage is unknown, but recent molecular analyses are consistent with gnetophytes being a sister group

Major clades within angiosperms

• Molecular data are not consistent with classification of flowering plants into two clades: monocots and dicots
• Monocots represent a monophyletic group based on DNA sequence data and
  • Leaves with parallel veins
  • Embryo with single cotyledon
  • Stems with scattered vascular bundles in cross section
  • Adventitious root system
  • Some "monocot" characters occur in non-monocots that are basal to angiosperms
    • three-merous flowers in two perianth whorls
    • herbaceous habit
    • monosulcate pollen
• "Dicots" are a paraphyletic group
  • Many typical dicot features are found in symplesiomorphic (shared ancestral characters) with gymnosperms
    • two cotyledons
    • persisent primary root derived from embryonic radicle
    • stems with vascular bundles in a ring in cross section
    • secondary growth (leading to woody habit)
    • reticulate, or net, leaf venation
  • Some dicots diverged prior to origin of monocots (i.e., ancient lineages that pre-date monocots), others diverged later (Figs. 8.1-8.5)
    • Sequence of divergence of ancient lineages is unclear, but among possible earliest branches off the angiosperm tree are
      • some woody groups (Magnoliales, Laurales, others)
      • some herbaceous groups (Nymphaeales, Ceratophyllales, Piperales)
      • generally have:
        • ethereal oils (10 and 15-C terpenoids) in spherical oil cells
        • elongate vessel elements with slanted end walls and scalariform perforation plates
        • radial flowers
        • free carpels and stamens
        • undifferentiated style with lateral stigma
        • monosulcate pollen
        • tiny embryo with abundant endosperm
  • One group of "dicots" (tricolpate angiosperms, or eudicots) appears to be monophyletic (Figs. 8.1- 8.6)
    • tricolpate pollen
    • loss of ethereal oil cells (scattered through parenchyma tissue)
    • Basal branches not well-resolved (Ranunculales, Caryophyllales+Polygonales, Saxifragales) (Fig. 8.7)
    • "Rosid" clade diverged from "Asterid" clade, but support for this split is relatively weak (Fig. 8.7)
      • "Rosids" split into two sub-clades (Fig. 8.7)
        • Oxalidales, Fabales, Rosales, Fagales
        • Brassicales, Malvales, Sapindales
    • "Asterid" clade split into 2 subclades (with a couple groups basal to those groups) (Fig. 8.8)
      • Solanales, Gentianales, Lamiales
      • Apiales, Asterales