Start with the water mollies actually want
Mollies are fish of coastal lagoons and slow rivers, and in aquariums they do best in hard, alkaline water that many fashionable aquarium plants quietly hate. That single fact decides the planting list. A plant that melts within a month in molly water is not a molly plant, however pretty it looked in the shop, so build the scape from species that genuinely enjoy mineral-rich conditions and shrug off the steady grazing mollies do all day long.
The dependable core planting
Vallisneria is the classic molly plant: its long ribbon leaves thrive in hard water, send out runners freely, and give the fish a forest to weave through at the back of the tank. Java fern and Anubias, tied to rock or wood, add tougher mid-level leaves that mollies investigate but rarely damage. Hornwort and water sprite grow fast enough to outpace nibbling, absorb waste nutrients, and can be left floating or loosely planted. Amazon sword plants also manage well once established, their roots appreciating the minerals that softer-water plants find excessive. Together these give you height at the back, texture in the middle and movement at the surface without a single fragile stem.
Planting for fry, because mollies breed
A molly tank with both sexes is a fry tank sooner or later, and planting is the difference between a handful of survivors and a tank overrun. Dense, fine growth is what newborn mollies need in their first days: a floating mat of guppy grass, a thicket of Java moss in a rear corner, or hornwort left to tangle at the surface. Adults will hunt fry through open water but lose interest quickly in dense cover, so even one generous refuge patch raises survival dramatically. Keep the refuge permanent rather than adding it when a female already looks ready to drop.
What to avoid, and the grazing question
Leave cabomba, most rotala and other soft-water stem plants on the shop shelf; they typically yellow and disintegrate in alkaline water, fouling the tank as they go. Expect mollies to rasp algae and biofilm from leaves constantly — that grazing is normal and even useful, and tough leaves handle it fine. Truly soft new growth may get trimmed by hungry fish, so feed vegetable matter regularly and the mollies will spend less of their grazing energy on your planting. Trim Vallisneria runners before they swamp the front glass, and thin floating growth so light reaches the plants below. Mollies also appreciate some open surface within that floating cover — they feed at the top of the water and rise to breathe and browse there — so keep a clear feeding ring rather than letting hornwort mat wall to wall. Moderate light over long hours suits this whole plant list; none of it needs specialist lamps, and algae on the glass will tell you honestly if the day has grown too long.
A molly tank usually ends up maintained by more than one person in a household, and KinsLe's Family Sharing keeps the plant list, feeding notes and water-change routine on the molly's shared profile, so whoever trims the Vallisneria this week works from exactly the same details as everyone else.