Emersed-Grown Plants: The Transition to Submersed Growth

Why nurseries grow aquarium plants above water, how aerial and submerged leaves differ, why emersed leaves die back after planting, typical timelines and how to support the switch.

Why nurseries grow plants emersed

Many plants sold for aquariums are amphibious in the wild: they can live both above and below the water surface as water levels change with the seasons. Hygrophila difformis, for example, forms serrated leaves on land and dissected leaves under water (Horiguchi et al., AoB Plants, 2019), and many Cryptocoryne species grow in lowland forest streams, in seasonally flooded forest pools or on river banks that are submerged only at high water (Wikipedia, Cryptocoryne).

Commercial production commonly imitates the dry season: amphibious plants are grown with only the roots in water, in pots of mineral wool, in greenhouses with controlled temperature and humidity and with artificial light. Growers state that plants raised this way build up reserves that they later use to form new leaves under water. Strictly aquatic plants such as Egeria, Cabomba and Vallisneria are usually cultivated submerged. A third form, very young plants grown in vitro in a laboratory, is sold in sealed cups and marketed as free of snails, algae and pesticides.

Aerial and submerged leaves are different organs

The ability of one plant to form different leaves in different environments is called heterophylly. It is widespread among land plants and especially common in aquatic and amphibious species (Li et al., Plants, 2019). Ranunculus aquatilis is a classic example: underwater its leaves are divided into thin strands, while at or above the surface it forms broad, only partly divided blades (Wikipedia, Heterophylly). Hygrophila difformis, whose leaf shape responds to plant hormones such as ABA, ethylene and gibberellin, is an emerging model species for studying this switch (Li et al., 2019; Li et al., Scientific Data, 2025).

Submerged leaves are typically thin, narrow, filamentous or linear, with reduced vascular tissue, and usually lack a cuticle and stomata, so gases and nutrients are exchanged directly with the water.
Aerial leaves are thicker and broader, covered with a cuticle and equipped with stomata.
In Hippuris vulgaris, aerial leaves have a thick cuticle, irregular rounded cells and numerous stomata, whereas submerged-type leaves have a thin cuticle, long thin cells and no stomata.

The switch is controlled by plant hormones and environmental signals. In the review by Li et al., ethylene induced submerged-type leaves in Ludwigia arcuata even in air, while abscisic acid (ABA) induced aerial-type leaves under water; ABA also induced stomata and cuticle formation in several Myriophyllum and Proserpinaca species. Light intensity and quality, photoperiod, temperature, humidity and osmotic conditions also influence leaf form in different species.

What happens after planting

A study of Hygrophila difformis (AoB Plants, 2019) followed leaves of terrestrially grown plants after submersion. Their underwater photosynthesis rose significantly within 5 days, partly because they acquired an intermediate ability to use bicarbonate, but their anatomy did not change. Fully submerged leaves of the same species were thinner, had fewer stomata on the lower surface, used bicarbonate more effectively and had a higher rate of oxygen evolution. In other words, an existing aerial leaf can partly acclimate, but the fully adapted form appears only in leaves that develop under water.

This is why emersed leaves are often lost while the plant produces new submerged growth. In Cryptocoryne the loss can be complete: the phenomenon known as crypt melt, in which a newly planted crypt drops all its leaves, is thought to be triggered by rapid environmental change, and nursery cultivation in emersed form followed by submersion is one suspected cause. Such plants may need about 30 days to establish and regrow leaves (Wikipedia, Cryptocoryne).

Expected timeline

First days: existing aerial leaves may increase their underwater photosynthesis but do not change shape (Hygrophila difformis, significant rise within 5 days).
Following weeks: the fully adapted form appears only as new leaves develop under water, so the plant's appearance changes as submerged growth replaces aerial leaves (Horiguchi et al., 2019).
About 30 days: time Cryptocoryne may need after melt to become established and regrow leaves (Wikipedia).

Supporting the transition

Before planting, rinse plants under tap water and remove as much of the mineral wool from potted plants as possible.
Nursery guidance commonly suggests little or no fertiliser in a new aquarium during the first weeks, since plants bring reserves from cultivation for the rooting phase.
Nursery guidance also commonly suggests a shorter photoperiod during the first weeks, increased gradually afterwards.
Fast-growing auxiliary plants placed alongside the main planting can take up surplus nutrients while the main plants adapt, and can be removed stepwise later.