Dwarf Grass-wrack

This species has long strap-shaped leaves, rounded leaf tips and thin rhizomes that are <3 mm in diameter. There are visible cross-veins in the leaf. The rhizomes are either dark brown or yellow. Young rhizomes are typically yellow, but the leaves of this plant can turn red if they're under high sunlight. Because of its phenotype, Z. muelleri can be confused with Z. tasmanica and Z. capensis. The leaf width morphology is variable, so Z. muelleri with thin leaves can sometimes also be confused with H. uninervus.

Zostera muelleri is a perennial species, meaning populations of it endure year round. They are mostly found in places such as littoral or sublittoral sand flats, sheltered coastal embayments, soft, muddy, sandy areas near a reef, estuaries, shallow bays, and in intertidal shoals. They aren't common on reefs because there is little space and nutrients for them to grow there. Zostera muelleri is a marine species, but it can tolerate some freshwater inputs. It mostly occurs in mono-specific meadows, but it can grow alongside Ruppia, Halophila, and Lepilena. Zostera muelleri is widespread in Southern Australia, and its also found in New Zealand and Papua New Guinea.

Seagrasses are flowering species, but they can reproduce both sexually and asexually. Reproducing sexually increases genetic variation, which can enhance a plant's ability to adapt to a changing environment, but asexual reproduction requires less effort and is what Z. muelleri typically uses to maintain its population. When reproducing sexually, the plant's flowers form an inflorescence that is enclosed in a spathe (a large sheathing bract that encloses flower clusters in certain plant species). Each shoot can have up to 6 spathes, which contain 4–12 pairs of male and female flowers. Larger plants will have more flowers. Male flowers typically mature before female flowers. Once a flowering shoot matures, it darkens and breaks off the plant, and floats away. The enclosed seeds then become deposited in sediment someplace else. Zostera muelleri can reproduce asexually via rhizome encroachment, which is a form clonal reproduction. The plant can use this form of regeneration to recover from high intensity disturbances.