Stockmansella is a genus of extinct plants of the Middle Devonian (Eifelian stage, around ), fossils of which have been found in north-west Germany. The sporophyte generation

Alternation of generations

Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...

 consists of prostrate dichotomizing stems (axes) up to 10cm long and around 3mm wide, which at intervals produce narrower smooth upright stems. These bear sporangia

Sporangium

A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...

 (spore-forming organs) on short lateral branches (sporangiophores). The prostrate stems have bulges from which rhizoid

Rhizoid

Rhizoids are thread-like growths from the base or bottom of a plant, found mainly in lower groups such as algae, fungi, bryophytes and pteridophytes, that function like roots of higher plants ....

s form. Both prostrate and upright stems have a central strand of conducting tissue which contains simple tracheid

Tracheid

Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast...

s, so that Stockmansella is a vascular plant

Vascular plant

Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...

.

The genus was created by Fairon-Demaret for fossil forms previously assigned to Taeniocrada

Taeniocrada

Taeniocrada is a genus of extinct plants of Devonian age . It is used as a form genus for fossil plants with leafless flattened stems which divided dichotomously and had prominent midribs regarded as containing vascular tissues...

but which differ in having single lateral sporangia. (She initially gave the genus the name Stockmansia, but this had already been used for a genus of ferns.) The form genus

Form taxon

Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships...

 Sciadophyton is thought to be the gametophyte

Gametophyte

A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....

 stage of several early land plants, including Stockmansella, although as these forms have only been found as compressed fossils, their morphology is not entirely clear.

In 2004, Crane et al. published a cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 for the polysporangiophyte

Polysporangiophyte

Polysporangiophytes, also called polysporangiates or more formally Polysporangiophyta, are plants in which the spore-bearing generation has a structure of branching stems terminating in sporangia...

s, in which Stockmansella is placed in the Rhyniaceae, sister to all other tracheophytes (vascular plants).