Spikemosses

Order Selaginellales

The spikemosses exist as a single genus, Selaginella, with about 700 living species. They are a creeping group of plants, growing on the floor of many tropical and subtropical forests, in wetlands, as well as rock outcrops in temperate and alpine regions. Some species grow as a rosette in seasonal dry habits. During the dry period, the plants curls inward on itself, becoming brown and nest-like in appearance. When moisture returns, the plants uncurls to the green, rosette form. These plants have been named "resurrection ferns" in the nursery trade.

Above: Stems and leaves of Selaginella sp.

Sporophyte (=spore-producing) phase

Vegetative features

Stems

Plants are herbaceous (not woody)
Branching is mostly anisotomous
Anatomy is protostelic, siphonostelic, or plectostelic

Leaves

Lycophylls or microphylls, usually in a planated fashion along the stem
Exhibit a scale-like ligule on microphylls and sporophylls

Roots

Most roots are mostly adventitious, created at points of branching
A leafless axis is created from an angle meristem and grows toward the soil
- This axis is called a rhizophore and produces roots at the distal tip.
  - Rhizophores are also found in extinct members of the lycopods (Drepanophytes)
- This rhizophore axis does not have a root cap, and can develop into a leafy shoot. This organ is unique and possesses features different from roots or shoots.

Reproductive features

Spore cases (sporangia)

Adaxial on sporophylls
Clustered into a cones
Heterosporous with megasporangia and microsporangia

Gametophyte (=gamete-bearing) phase

Small, but multicellular gametophytes
Mega- and micro-gametophytes are endosporic (not released from spore)
They are also heterotrophic and not photosynthetic
- Supply of nutrients is limited to what is contained in the original spore.
- Development in males is limited to the formation of an antheridium (sterile jacket) containing up to 32 sperm.
- Female gametophyte is larger and creates archegonium and rhizoids
- Sperm are released and swim to the female gametophyte for fertilization