Warning. Science bomb ahead!! At Green Lady Gardens, we love the science behind plants. Selaginella are especially interesting due to a number of unique and rare characteristics. (Read to the very bottom to understand why that expensive Albo Monstera you purchased has never ever grown!.)
Spike mosses (Selaginella spp.), also known as club mosses, are vascular plants. They are not true mosses, which are non-vascular. Vascular plants have stems, roots, and leaves which contain a "tubed" vascular system. That system transports water and food from the roots to the leaves through tissue called 'xylem', and food from the leaves to all other parts of the plant through tissue called 'phloem'. On the other hand, non-vascular plants do not have a vascular system. They absorb water and nutrients from their damp environment through osmosis. Water and nutrients are then transported throughout the plant from cell to cell via diffusion.
Selaginella are unique in that they have rhizophores. Rhizophores are shoots that grow down from where the plant's leaves branch, and they turn into branching roots once reaching the soil.* Rhizophores are used as an anchor, to feed, and in reproduction as leaves & branches that break off of the mother plant can grow roots. (This makes propagating spike moss easy.) Rhizophores are unique to Selaginella. There are approximately 750 known Selaginella species out of anywhere from 400,000 to 435,000 known land plant species, depending on how you count them.
Selaginella are also interesting because most vascular plants have seeds. Vascular plants that have spores instead of seeds are called lycophytes. Selaginella are, you guessed it, lycophytes. (Ferns are also vascular plants with spores instead of seeds but their leaf structure is different so they have a different classification, monilophytes.)
*Rhizophores are different than aerial roots. Aerial roots grow above ground and their primary purpose is to support and "adhere" the plant to a support (such as a wall) or another plant in an epiphytic-like way. Aerial roots can grow in soil but it is not common. It is even less common for them to branch into soil roots in the way rhizophores do. Aerial roots also cannot be used for reproduction. A node is required for the growth of cells, branches, leaves, and stems. If you're about to invest in an expensive propagation that has a single, long, and beautiful aerial root, make sure it has a node first!
If you read all of that, it's official. You're a plant nerd. Welcome to the club!
Light
Bright indirect (in a not too hot location) is best. Will tolerate lower light if given bright morning light. Direct sun exposure causes leaf scorch.
Humidity
High. Increase with a humidifier, pebble tray, or enclosure. Do not mist. Low humidity = browning leaves. Keep from heat vents & high temp areas, which are drying.
Water
Water when plant droops or when top soil is dry to the touch. Soil should be damp, not soggy. Bottom watering is the most effective, but don't let it sit too long. Drooping & revival happen suddenly, within hours. Overwatering = leaves droop, wilt, & die. If plant droops b/c soil is dry & gets watered but continues to droop, it was overwatered. Underwatering = curled, brown, crispy leaves. Spike moss with dry soil and low humidity.
Soil & Repotting
Requires a well-draining but moisture-retaining soil, such as a peat moss based soil with perlite. Repot when plant requires more frequent watering. Pot must have drainage.
Propagation
Easy due to root growth from stems. Lightly bury the rhizophores in soil to grow roots. (Read more in blog intro paragraph.)
Temperature
Average household, 50-75°F. Minimum 40°F.
Keep from high temps & hot & cold drafts.
Pruning
Prune to promote bushy, compact growth.