Basal Seed Plants

Oldest known spermatophytes

Seed plants appear in the fossil record in the Famennian of the Late Devonian with many different species and forms. The earliest seed-like plants occur in the upper Middle Devonian. The "preovules" (paraovules) were small, radially symmetrical, and usually surrounded by a cupule. These preovules were composed of a megasporangium/nucellus surrounded by an integument, but the integument was not complete. The preovule bears an unopened distal extension protruding above the multi-lobed integument, which is assumed to be involved in wind pollination. Evolution during the middle to late Devonian was creating many different forms of seed-like structures, which were being selected for greater protection of the female gametophyte and eventually the embryo.

It is assumed that from these preseed plants evolved a true seed plant that had a complete integument surrounding the nucellus.

Geologic Age

Late Devonian (Famennian) - Early Carboniferous

Systematics

└Lignophytes

Above: Late Devonian seed morphologies, a) Moresnetia-type, b) Dorinnotheca-type, c) Warsteinia-type, d) Aglosperma-type, e) Condrusia-type (from Prestianni & Gerrienne 2010 [Fig. 3])

Aglosperma †

Hilton & Edwards, 1996
Famennian of the UK
Preovules

A. quadrapartita

Hilton & Edwards, 1996

A. avonensis

Hilton, 1998

Alasemenia tria †

Wang et al. 2024
Famennian of Anhui Province, China
Dichotomous branches bearing terminal and acupulate ovules
Three broad wing-like integumentary lobes radially and symmetrically attached to each nucellus, distally tapered and proximally reduced.
Integumentary lobes evidently extending outwards, with their free parts ca. 40% of ovule length.
Individual integumentary lobes folding inwards along abaxial side. Nucellus largely adnate to integument.

Archaeosperma arnoldii †

Famennian of Pennsylvania
Pettitt & Beck, 1968
Branching systems ("Moresnetia-type") bearing cupules with seeds
Cupule had 5-6 broad lobes

Condrusia †

Stockmans, 1948
Famennian of Belgium & Russia
Seeds are enclosed in a well-developed wing, composed of two flat cupule segments adpressed against each other

C. brevis

- Petrosyan in Lepekhina et al., 1962
- Famennian of Russia

C. minor

- Stockmans, 1948
- Famennian of Belgium

C. rumex

- Stockmans, 1948
- late Famennian of Belgium

Cosmosperma polyloba †

Wang et al., 2014
Famennian of South China (Wutong Formation, Changxing County)
Cupulate ovules: one ovule surrounded by up to 16 distal segments and with minute spines on the outer surface
Synangiate pollen organs bearing six to eight microsporangia fused only at the base,
Planate and highly dissected pinnules in alternate arrangement

Dorinnotheca streelii †

Fairon-Demaret, 1996
Famennian of Belgium
3-4 integument lobes around nucellus
Cupule is large with 8 proximally-fused parts, forming a cup; distal ends are divided into at least 40 free tips
Cupule may aid in wind dispersal

Above: Fertile branches and seeds of Alasemenia tria

Below: reconstruction and compression of Archaeosperma

Above: Reconstruction of Cosmosperma

Elkinsia polymorpha †

Rothwell et al., 1989; Serbet & Rothwell, 1992
Late Devonian of West Virginia
Elkinsia has an unbranched stem, with pinna-bearing fronds proximally on the plant
- Stems are terete with three-ribbed centarch protostele, maturation of other protoxylem marginally mesarch.
- Fronds helically arranged, composed of terete rachides with papillionoid, C-shaped bundles proximally and circular bundles distally, vegetative fronds with sphenopterid pinnules
Distally, the plant displays "fertile cruciately forking fronds with terminal cupules or prepollen organs" (Serbet & Rothwell 1992)
- There are four (pre)ovules born in each cupule (=cup-like branch system surrounding ovule)
- These ovules are considered "preovules" since the integument "...does not completely surround the nucellus to form a functional micropyle" (Serbet & Rothwell 1992)
- There are 16 sterile branch tips surrounding preovules

Guazia dongzhiensis †

Wang et al., 2021
Late Devonian (Famennian) of China
This ovule is apparently without a cupule, unlike other Late Devonian seeds.
Dichotomous fertile branches bearing terminal ovules
Ovules elongate, obovoid, radially symmetrical and lacking a cupule
Four broad wing-like lobes as integumentary outgrowths cruciately-arranged in each ovule, distally tapered, and proximally reduced
Individual integumentary lobes folding inwards along abaxial side
Free parts of integumentary lobes 30%-40% of ovule length
Nucellus present except for near apex adnate to integument
Nucellar apex dome-shaped.

Glamorgania gayerii †

Famennian of Wales
Hilton, 2006
"Moresnetia-type" seed

Hydrasperma tenuis †

Matten et al., 1975
Famennian
The cupules containing 2–6 seeds are borne in pairs.
Each cupule is campanulate and composed of up to 24 oval to terete units.
The axis of the cupule is forked, each resultant branch dividing in an alternate monopodial fashion producing six major axes

Above: Hydrasperma reconstruction

Kerrya mattenii †

Famennian of Ireland
Rothwell & Wight, 1989
"Moresnetia-type" seed

Latisemania longshania †

Wang et al., 2015
Late Devonian (Famennian) of the Wutong Formation of China
Cupulate ovules that are terminal and opposite on the fertile axis
Associated foliage (not attached) is Sphenopteris-like

Lenlogia krystofovichii †

Famennian of Russia
Krassilov & Zakharova, 1995
"Moresnetia-type" seed

Moresnetia zalesskyi †

Stockmans, 1948; Fairon-Demaret & Scheckler, 1987
Found in Belgium
Branching systems bearing cupules with seeds
- Cupule had 8-10 thin lobes

Pseudosporogonites hallei †

Famennian of Belgium
Stockmans, 1948
"Aglosperma-type" seed

Above: Reconstruction of Moresnetia

Below: Cupules of Glamorgania gayerii. From Hilton, 2006, Plate III.

Telangiopsis sp. †

Wang et al., 2016
Upper Devonian (Famennian) Wutong Formation, Dongzhi County, Anhui Province, China
Pollen organ associated with, but not attached to, vegetative fronds
Fertile axes with terminal pollen organs are dichotomous for 2-4 times, and may be proximally attached by fragmentary pinnules
Pollen organs are synangiate and borne on the top of a short stalk
- Synangia are radial in symmetry, and each consists of 4-8 elongate microsporangia fused at base.
- Microsporangia have a longitudinal dehiscence line and show a tapered apex
The associated stem is spiny and bears a vegetative frond which bifurcates once at the basal-most part.
- Frond rachises possess one order of pinna arranged alternately
- Pinnules are borne alternately, planate, highly dissected, and equally dichotomous for 2-3 times.
Telangiopsis sp. reinforces that the Late Devonian pollen organs are synangiate usually with basally fused microsporangia.

Warsteinia paprothiae †

Rowe, 1997
Famennian of Germany
Preovule that lacks a cupule
The integument has four winged lobes that are fused to the nucellus
- Possible indicator of wind, maybe water, dispersal (anemochory)

Xenotheca †

Arber & Goode, 1915
Famennian

X. devonica

- Arber & Goode, 1915; Hilton & Edwards, 1999
Famennian of the UK
"Moresnetia"-type seed

X. bertrandii

- Stockmans, 1948
- Famennian of Belgium
"Aglosperma-type" seed

Above: Hilton, 2006, Plate I. Cupules and preovules of Xenotheca devonica from the Late Devonian Taffs Well plant bed.

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