Abstract Detail

Fossil plants at the intersection of evo-devo and phylogeny: celebrating the contributions of Gar W. Rothwell to biodiversity and evolution

Raymond, Anne [1], Costanza, S H [2], Correa, Julian [1].

A bisporangiate cordaitean cone from the mid-Pennsylvanian of Iowa.

A new cordaitean cone from the mid-Pennsylvanian of Iowa consists of a primary cone axis with attached secondary fertile shoots: one apical, one lateral, each approximately 10 mm long and 4 mm in diameter. As in most cordaitean cones, sterile sclerenchymatous and transitional scales occur at the base of the secondary fertile shoot. Distal to these are approximately 25 parenchymatous, rod-shaped male scales with remnant pollen sacs. The uppermost male scale has a ring of 4 or 5 developing pollen sacs at the tip. Approximately 15 upper sterile scales occur distal to the male scales; these are erect, parenchymatous and crescent-shaped in cross section. The apical scale is similar in shape and bears a single, orthotropous seed, adaxially attached to the base of the scale. We identify the attached organ as a seed based on the presence of three nested membranes and portions of a fourth: 1. The exterior membrane, interpreted as the exterior cuticle of the developing seed, is visible 100 μm above the base of the fertile scale. This membrane encloses thin-walled tabular cells and tracheids of the seed’s integumentary vascular system; its cuticle has inward pointing anticlinal cell-wall fragments. 2. At the apex of the developing seed, a partial membrane is interpreted as the inner epidermis of the endotesta. 3. The third membrane, interpreted as the exterior cuticle of the nucellus, has cuticle with inward pointing anticlinal wall fragments and forms a blunt tip near the seed apex, interpreted as the base of the nucellar beak. 4. The interior membrane, interpreted as the magagametophyte membrane, encloses tracheids with reticulate secondary walls, interpreted as an embryo.
The new cone comes from the diverse cordaitean assemblage of North America, which contains three cordaitean seed genera: Cardiocarpus, Mitrospermum and Nucellangium. We identify the attached seed as Nucellangium based on the integumentary vasculature and nucellar cuticle. We eliminate Mitrospermum and Cardiocarpus respectively, based on pollen sac and seed attachment to the fertile scales.
We have eight specimens of the new cone, including two compound cones and eight secondary fertile shoots with attached ovules, four with fertile male scales. Its morphology closely matches the pollen cone, Cordaianthus shuleri (Darrah) Fry, except that C. shuleri has multiple male scales rather than a single seed scale at the tip. The Nucellangium plant may have had andromonoecious reproduction with male only pollen cones and bisexual seed cones.

1 - Texas A&M University, Dept. of Geology & Geophysics, Texas A&M University, College Station, Texas, 77843, United States
2 - 35 Columbia St, Malden, MA, 02148, United States

Keywords:
Cordaitean bisexual cone
mid-Pennsylvanian
Nucellangium
Cordaianthus shuleri (Darrah) Fry
andromonoecious.

Presentation Type: Colloquium Presentations
Session: C11a, Fossil plants at the intersection of evo-devo and phylogeny: celebrating the contributions of Gar W. Rothwell to biodiverstiy and evolution Part 1
Location: 110/Mayo Civic Center
Date: Wednesday, July 25th, 2018
Time: 9:00 AM
Number: C11a003
Abstract ID:682
Candidate for Awards:None