Origin of Angiosperms

clearly derived features/characteristics of angiosperms (5)

• carpels

• stigmatic pollen germination

• reduced gametophytes

• endosperm

  • double fertilization

  • delay investment

carpels

megasporophylls that are infolded and enclose the ovules (immature seeds)

provide protection to ovules

stigmatic pollen germination

germination occurs on the stigma rather than directly on the ovule

allows for greater selectivity of reproductive partners by maternal parent

reduced gametophytes

microgametophytes = pollen tubes

• only 3-celled at maturity, a tube cell, and 2 sperm cells

megagemtophytes

• 7-celled, 8-nucleate embryo sac

endosperm

a nutritive tissue that develops from a second fertilization event

one of the two sperms from the pollen tube unites with two polar nuclei of megagametophyte

double fertilization

involvement of both sperms in fusions with different cells of the megagametophyte

angiosperms __________ __________ in nutritive tissue for each embryo until fertilization is assured

delay investment

Darwin’s abominable mystery

The mystery was how to account for what appeared to be a sudden appearance of modern angiosperm families in the Cretaceous. Transitional fossils appeared to be absent.

Today, there is still no evidence of verifiable angiosperm fossils before the early Cretaceous. Why?

Fossil evidence suggests that angiosperms rapidly displaced other groups of seed plants during the Cretaceous.

The fossils from the early Cretaceous show evolutionary transitions in leaf and pollen characteristics. What does this mean?

Modern angiosperms do not suddenly appear.

Until recently angiosperms were widely believed to be the sister group of ____________ based on preliminary molecular and morphological phylogenetic analyses. 

gnetophytes

More recently, phylogenetic results from multiple-gene analyses provide more support for a sister-group relationship between ___________ and _________.

gnetophytes and conifers

• both share various morphological features, such as compound seed cones

5 major groups of seed plants

• cycads

• ginkgos

• conifers

• gnetophytes

• angiosperms

ANITA grade

Amborella

Nymphaeales

Illiciales

Trimenia

Austrobaileya

The features below are shared by some or all of the different lineages of the ANITA grade and are therefore suggested to have been features found in the most recent common ancestor of all living angiosperms:

• Two cotyledons (dicots, not monocots)

• Uniaperturate pollen (not triaperturate)

• Carpels sealed by secretions (not fused); ascidiate (barrel-shaped)

• Lack of differentiation of sepals and petals (tepals)

• Indeterminate (variable) numbers of tepals, stamens, and carpels

• Spiral arrangement of floral parts

• Lack of fusion of floral parts

• Self-incompatibility = pollen cannot fertilize ovules from the same plant

• No vessels (but other vessel-less angiosperms (e.g., Winteraceae) evidently represent a loss of vessels)

• Occurrence in sporadically disturbed sites in shady forest understories ("Dark and Disturbed" ecology)

Early Angiosperms covered in basal angiosperm lab

Amborellales

• Amborellaceae – Amborella family (Amborella trichopoda). 1 genera/1 species.

Nymphaeales

• Cabombaceae

  • Cabomba caroliniana (fanwort)

  • Brasenia sherberi (water shield)

• Nymphaeaceae

  • Nymphaea odorata (Water-Lily)

  • Nuphar advena (broad leaf pond lily)

  • Nuphar variegata (Bull-head lily)

Austrobaileyales

• Illiciaceae

  • Illicium floridanum (Florida star anise)

Magnolids covered in basal angiosperm lab

Laurales

• Calycanthaceae

  • Calycanthus floridus (sweet shrub)

• Lauraceae—Laurel family (L. laurus, laurel or bay). 45 genera / 2200 species.

  • Sassafras albidum (sassafras)

  • Lindera benzoin (Northern spice bush)

  • Persea (avocado)
    

Magnoliales

• Annonaceae—Custard-Apple family (Anona, a Haitian name). 112 genera / 2150 species.

  • Asimina triloba (Pawpaw)

• Magnoliaceae—Magnolia family (after Pierre Magnol of Montpellier, 1638–1715). 7 genera/200 species.

  • Magnolia grandiflora (flowering magnolia)

  • Magnolia fraseri (mountain magnolia)

  • Magnolia macrophylla (big leaf magnolia)

  • Lirodendron tulipifera (tulip tree)

Piperales

• Aristolochiaceae - Birthwort family (Gr. aristos, best + lochia, childbirth, from resemblance of a species of Aristolochia to the correct fetal position). 7 genera / 410 species.

  • Aristolochia sp.

  • Asarum canadense (Canadian Wild Ginger)

• Piperaceae—Pepper family ( piper, Indian name for pepper). 14 genera/1940 species.

  • Peperomia (Peperomia)

  • Piper sp. (pepper, stem in slide only)