Corystosperms †

Ecology & Form

• Major plant in Triassic ecosystem; index fossil 

• Replace glossopterids in the flora

• Probable affinities with Medullosa and cycads based on wood anatomy (Artebe & Brea 2003)

• Possible ancestor-descendant relationship with Ginkgo (Shi et al. 2016)

• Once thought to have a possible link to the angiosperms based on ovule, but recent evidence doesn't support this (Klavins et al. 2002; Soltis et al. 2005) 

Stem

• Permineralized woody stem (Rhexoxylon) up to 70 cm in diameter

  • Primary xylem bundles produce wedges of wood on both sides.

  • Cambium growth was staggered and not synchronized

• Wood morphotaxa: Jeffersonioxylon and Kykloxylon

• Distinctive short shoots

• These were small to large palm-like, but deciduous trees living in seasonally flooded (monsoon) environments

Leaves

• Pinnate leaves (Dicroidium)

• Several types of foliage

• All pinnate

• Open dichotomous venation

Pachypteris

• Hypostomatic, bipinnate or unipinnate leaves, with alethopteridian venation (midvein and secondary veins divided once or twice before reaching the pinnule margin), pinnules with entire margins and rounded apices

• The stomata are haplocheilic, monocyclic or dicyclic, usually depressed, with the guard cells occurring in the lowermost part of the stoma.

Komlopteris 

• Leaves pinnate, pinnules in opposite or alternate position, elliptical-elongated or elongated in outline, apex acute or subacute to rounded, margins entire, occasionally slightly undulate

• Venation alethopteroid, the midrib more or less symmetrically situated in the middle of the pinnules. 

• Secondary veins simple or irregularly once or twice forked

• Leaves stiff, coriaceous, strongly cutinized. Cuticle thick; cuticle of lower leaf surface usually thinner than that of upper leaf surface

• Pinnules amphistomatic with only a few stomata on the upper leaf surface

• On the lower leaf surface stomata are situated in intercostal bands between well-marked veins

• Stomatal complexes amphicyclic, consisting of two guard cells situated near the surface of the leaf and 5-7 subsidiary cells which are divided by a thick line into 2-3 narrow concentrical rings around the stomatal pit

• Sometimes stomata are surrounded by a more or less complete ring of encircling cells. 

Roots

• Unknown

Reproduction

Ovule structure (Umkomasia)

• Stalked and recurved

• Helmet-like cupules

• Opposite on stems

• Abaxial position (unlike adaxial position of angiosperms)

Pollen structures (Pteruchus)

• Alternately born on short axis

• Microsporangia on abaxial side of flattened circular lamina

Diversity

• Dicroidium †

• Pterusuchus †

• Umkomasia †