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Seed fern with large seeds
Seed fern with large seeds
The Medullosales are a strange group of Late Paleozoic seed plants with fern-like foliage. These plants had pulpy seeds the size of avocado pits. In addition they had large, wing-less pollen. These features seems to indicate that these plants employed animals for pollination and/or dispersal, which would make this group the first on Earth to have such a symbiosis. In many phylogenetic studies, the medullosids are a sister group or closely-related to the cycads.
Ecology & form
Ecology & form
Tree fern-like growth
Possibly grew in arid and wet env'ts
Late Pennsylvanian–early Permian medullosids were thriving under seasonally-dry climate on wet, rocky soils showing proximity to the groundwater level (Luthardt et al., 2021)
In forested landscapes, they occurred as part of the forest understory.
Permian medullosids probably had a (semi-)self-supporting growth habit with a high water-conducting potential of these plants. Anatomical differences with tropical relatives of Carboniferous age might reflect an evolutionary process that was driven by environmental changes during the late Paleozoic (Luthardt et al., 2021).
Classification
Classification
└Medullosales †
Geologic Age
Geologic Age
Plant-Animal Interactions
Plant-Animal Interactions
Several damage types (DTs) on leaves include margin feeding, hole feeding, and surface feeding, but also galling, piercing, and sucking, as well as oviposition scars (Molina-Solís et al., 2023)
Carboniferous taxa had adaptations such as curved and glandular trichomes that probably helped to dissuade invertebrates from predating them
Stems
Stems
Persistant leaf bases (Medullosa †)
Leaves
Leaves
Large fronds with bifurcate petiole (Myeloxylon †)
Some pinnae, in the form genus Neuropteris †, are broad, with a thin epidermis, uniform mesophyll, numerous stomata, and lack papillae and hairs
Other pinnae, in the form genus Alethopteris †, are narrow, with a thick epidermis and hypodermis and sunken stomata, as well as an adaxial palisade layer, abaxial spongy mesophyll, and epidermal hairs
Roots
Roots
Adventitious and prop-like
Classification
Classification
└Medullosales †
Geologic Age
Geologic Age
Reproduction
Reproduction
Ovule-producing structures
Avocado pit-sized seeds (Pachytesta † or Trigonocarpus †)
7 mm to 6 cm in length
Many layered seeds: fleshy outer layer, stony middle layer, and fleshy inner layer
Pachytesta †
Pachytesta †
Brongniart, 1874; Hoskins & Cross, 1946
P. crenulata †
Late Pennsylvanian
Large, ellipsoidal ovules, with three-layered integument (sarcotesta, sclerotesta, endotesta) with three commissured primary ribs most strongly expressed at the apex
Sarcotesta of three layers: the exterior cuticle suggests an epidermis of uniform parenchyma cells; a layer of irregular, randomly oriented parenchyma cells, which is lacunar near the exterior of the ovule; and an inner solid layer of tabular, radially-oriented parenchyma cells.
Sclerotesta of two layers: outer layer of interwoven sclerenchyma fibers that form longitudinal ridges; and an inner layer composed primarily of longitudinal fibers, with some fibers wrapping around the ovule perpendicular to its long axis, in a tangential direction.
Endotesta a thin cuticle except at ovule apex.
P. illinoensis †
P. duquesnei †
Middle Pennsylvanian, Bruay Formation, France
Carboniferous medullosalean ‘seed’ attributed to a female reproductive structure of Alethopteris
The peculiar micropylar extension of the new ‘seed’, as long as half of the total ‘seed’ length
A possible function of the extremely elongated micropylar extension suggests it is unlikely adapted to a pollination-drop mechanism, but rather...
...linked to a protection mechanism against arthropod predators
...and/or to a highly specialized pollination mechanism either by very tiny insects entering these ‘seeds’ through this tube (e.g. figs and fig wasps as modern analogs)
...or an insect with elongated mouthparts able to go inside the ‘seed’ (e.g. tube flower and moths with extremely long proboscis), to feed and transport pollen at the same time
If #2 or #3 provie accurate, this would be the earliest evidence of pollination in the fossil record
The attribution of Whittleseya elegans as male organs of an Alethopteris sp. is possible
Above: Reconstruction of Pachytesta illinoensis † (from Fig 4, Raymond & McCarty, 2009)
Pollen-producing structures
Clusters of elongate sacs formed into a variety of cup-, bell-, and cigar-shaped configurations (Aulacotheca †, Dolerotheca †, Potoniea †, and Whittleseya †)
Extremely large wingless pollen in most
May indicate required interaction with pollinators to disperse pollen
Anatomical evidence indicates they were borne on the fronds, attached to the rachis
Pollen is considered pre-pollen by some researchers since it displays a proximal trilete mark (as in Potoniea), and is assumed to germinate proximally, similar to microspores of spore-bearing plants
This is in contrast to the distal, equatorial, or other typical apertures of seed plant pollen grains.
Most other medullosids produced large ovoid pre-pollen with a monolete mark, and were assigned to the genus Schopfipollenites †.
Alethopteridaceae
Alethopteridaceae
Alethopteris †
Alethopteris †
Sternberg 1825
Pennsylvanian - Early Cretaceous
Pinna are narrow, with a thick epidermis and hypodermis and sunken stomata, as well as adaxial palisade layer, abaxial spongy mesophyll, and epidermal hairs
A. ambigua; A. crassa; A. evansi; A. halli; A. hartungi; A. lacoei; A. marginata; A. roesserti; A. serli; A. valida; A. whitney
Neuralethopteris †
Neuralethopteris †
Cremer 1893
Late Devonian - Pennsylvanian
N. biformis; N. lindahlii; N. pentias; N. pocahontas; N. schlehanii; N. sergiorum; N. smithsii
Lonchopteris †
Lonchopteris †
Brongniart 1828
Bi- or tripartite leaves similar to Alethopteris except with veins that display anastomoses or pseudo-anastomoses
Stomata are hypostomatic and anomocytic
L. bricii; L. virginiensis
Lonchopteridium †
Lonchopteridium †
Leaves similar to Alethopteris and Lonchopteris and occupying an intermediate morphology between these form genera
Cyclopteridaceae †
Cyclopteridaceae †
Laveineopteris †
Laveineopteris †
Callipteridium †
Callipteridium †
Margaritopteris †
Margaritopteris †
Douropteris †
Douropteris †
Neurodontopteridaceae †
Neurodontopteridaceae †
Neuropteris †
Neuropteris †
Reticulopteris †
Reticulopteris †
Odontopteris †
Odontopteris †
Macroneuropteris †
Macroneuropteris †
Neurodontopteris †
Neurodontopteris †
Neurocallipteris †
Neurocallipteris †
Barthelopteris †
Barthelopteris †
Lescuropteris †
Lescuropteris †
Palaeoweichselia †
Palaeoweichselia †
Parispermaceae †
Parispermaceae †
Paripteris †
Paripteris †
Linopteris †
Linopteris †
Above: Alethopteris leaf
Below: Neuropteris leaf
Above: Callipteridium leaf
Below: Linopteris leaf
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