Polysporangiophytes
Plants that branch in their spore-bearing phase
Above: This clade represents all land plants that have the ability to branch (in the sporophyte phase). This includes all living and extinct vascular plants (e.g. ferns, conifers, flowering plants, etc.), as well as a few extinct groups that lacked true vascular tissue (i.e. Horneophytes †)
Features
Exhibit apical branching in their sporophytes (spore-bearing phase of lifecycle)
Branching allows for multiple sporangia per plant, therefore the name polysporangiophyte or "many sporangia plant"
This is in contrast to the bryophytes, which have one sporangium per individual since their sporophytes do not branch.
Classification
└Viridiplantae
└Streptophytes
└Embryophytes
└Polysporangiophytes
Diversity
Polysporangiophytes include all vascular plants (Tracheophytes), as well as pre-vascular plants such as the extinct Eophytes, Horneophytes, and Aglophyton
Geologic Age
Silurian - present
Capesporangites petrkraftii †
Silurian of Czech Republic
Plant with dichotomously branched narrow leafless axes.
Sporangia terminal, vertically elongated, more than twice longer than wider, terminating in a cap-like structure at apex.
Gradual transition between sporangium and subtending axis.
Catenalis digitata †
Early Devonian (Pragian) of Yunnan China
Leafless axes bore 10-12 elliptical spore-forming organs or sporangia on side branches
To release their spores, the sporangia split at the opposite end to their attachment to the stem.
Its phylogenetic relationship to other land plants is considered uncertain at present.
Elandia itshoba †
Early Devonian of South Africa
Plant forming dense trusses of fine, smooth, isotomously branching axes bifurcating up to four times,
Axes bifurcating at a low angle and terminating in minute, elongate ovate sporangia; multiple axes united by a basal structure
Sporangia straight-sided with broadly rounded apices; 1.3–1.6 mm long and 0.4–0.7 mm wide
Above: Elandia itshoba † (Figure 9; Gess & Prestianni 2021)
Krommia parvapilla †
Early Devonian of South Africa
Plant with smooth, three dimensional, isotomously branching axes born singly and terminally; dichotomizing up to three times.
Branching angle variable (40°–110°).
First and second order axes U shaped.
Axes 1.5–3.0 mm long and 0.3–0.35 mm wide below sporangia.
Small constriction at junction between subtending axis and sporangium.
Sporangia small and rounded between 0.7 and 0.8 mm in diameter.
Above: Krommia parvapilla † (From Figure 9; Gess & Prestianni 2021)
Mtshaelo kougaensis †
Early Devonian of South Africa
Plant with multiple (at least 6) elongate sporangia, spindle-shaped in profile and evenly tapering to acute terminations, truncated proximally at point of attachment; arranged in a truss of sporangia that terminates elongate parallel sided isotomously bifurcating
Robust axes bifurcate at least twice and widen slightly towards the terminal truss of sporangia; individual sporangia 0.74 to 0.8 mm wide and 4–6 mm long with a longitudinal dehiscence line.
Vegetative axes 1.0 to 1.4 mm wide
Above: Mtshaelo kougaensis † (Figure 10; Gess & Prestianni 2021)
Pertonella †
P. dactylethra (Fanning et al. 1991)
Late Silurian of the Welsh Borderland
Plants branch isotomously (45 degrees)
1.1-1.3 mm wide
Axes end in a terminal sporangium 3mm wide
The axis/sporangium transition is abrupt
Sporangia are plate-shaped, transversely disposed
P. sp. (Gerrienne et al. 2001)
Above: Plate III (Gerrienne et al. 2001) showing Pertonella axes and sporangia
Steganotheca striata †
Silurian (Ludlow) of Powys, Wales (Edwards & Rogerson 1979)
Plant exhibiting elongate sporangium terminating a short length of parallel-sided, unbranched axis.
The diagnostic features of S. striata sporangia, the obliquely running striations and the terminal thicker lens-shaped region are usually clearly visible.
In the majority of specimens the distal region persists, the organic material of the main body of the sporangium has flaked off leaving dark strands adhering to the rock surface
Above: Plate 1 (Edwards & Rogerson 1979) showing Steganotheca striata sporangium showing surface striation
Tichavekia grandis †
Upper Silurian (Přídolí) of Czech Republic
This Silurian plant has multiple levels of isotomous branching (~5 levels) which is exceptional for the time
The first dichotomy divides the plant into two asymmetrical parts
Branches are ~1mm wide
It also is large for a Silurian plant, reaching up to 140mm in length
Axes terminate with paired sporangia generally ~2.5 mm in diameter, subsphaerical to ellipsod sacciform in shape,
Sporangia bear round structures 0.75 to ~1 mm in diameter.
Other details regarding in situ spores or conducting elements unknown
