Mosses stay small because they have no water-conducting vascular tissue

Evidence

Mosses are small because they lack any support system to hold them upright. Large mosses occur mostly in lakes and streams, where the water can support their weight. Trees stand tall and rigid because of their vascular tissue, the network of xylem, thick-walled tubular cells that conduct water within the plant like wooden plumbing. Mosses are the most primitive of plants and lack any such vascular tissue. Their slender stems couldn’t support their weight if they were any taller. This same lack of xylem means that they can’t conduct water from the soil to leaves at the top of the shoot. A plant more than a few centimeters high can’t keep itself hydrated. — Robin Wall Kimmerer, Gathering Moss, 89

Categorization

• XREF: Explains the size consequence flagged by the preschool kids; links to the wider theme of organism constraint architecture. — connects to: Mosses survive desiccation that would kill vascular plants by tolerating full drying — Robin Wall Kimmerer, Gathering Moss: A Natural and Cultural…, 175; The still-air boundary layer near the ground is thick enough to trap kites — Robin Wall Kimmerer, Gathering Moss: A Natural and Cultural…, 97; Mosses move water passively by harnessing surface forces rather than expending energy — Robin Wall Kimmerer, Gathering Moss: A Natural and Cultural…, 200 (+1 more)

Broader Connections

• Mosses move water passively by harnessing surface forces rather than expending energy #expands (0.85) — Robin Wall Kimmerer, Gathering Moss, 200
• Colonial packing, not individual form, is what holds water in moss #expands (0.75) — Robin Wall Kimmerer, Gathering Moss, 185