Useful Temperate Plants (6)  lists many edible uses for this species as follows: 

FLOWERS: A tea is made from the flowers. (6). "The following uses are recorded for Althaea officinalis, they are said to also apply to this species. Flowers - raw. Added to salads." (6).
SEEDS: The seeds might be used to produce an edible oil in the future. A 2013 Chinese study listed this species (synonym listed - virginica) as a "potential source of edible oil and proteins." (14).
LEAVES: "The leaves can be eaten raw but are rather fibrous and somewhat hairy, though the taste is pleasant. They are used as a potherb or to thicken soups. Leaves - raw or cooked." (6). 

ROOT:  "Raw or cooked.  A tea can also be made from the root, it is concentrated by boiling until it has a similar consistency to egg white. he water from the root is the most effective. The water left over from cooking any part of the plant can be used as an egg-white substitute in making meringues etc., it is also dried then ground into a powder, made into a paste and roasted to make the sweet 'marshmallow’. The root is used as a vegetable." (2). 

SEED = OIL = PAINTS and VARNISHES. (5). "It is a suitable feedstock for the production of biodiesel and ethanol with 22% oil content in seed." (11, 12). "Seeds of Kosteletzkya virginica (a synonym for this species) were composed largely of unsaturated fatty acids, high potassium, and low sodium." (13).
FIBER (from stems) for NETS, STRING. (5). 
ROOT = a GLUE. (5). 
IUCN writes, "Historially, the species (when the species together with  Hibiscus ponticus were abundant and widespread) was used for making of fibre and nets. A strong fibre is obtained from the stems. It is used for making string, nets, etc. A glue can be made from the root. An oil from the seed is used in making paints and vamishes." (5). 
It has been used for "reclamation of the salt-affected soils." (11). "The foremost merit of Kosteletzkya virginica is its strong salt resistance. It was reported that it was able to complete growth and development normally in soil with 0.3 to 2.5% sodium salt (mainly NaCl)." (11). 

Dr. Craig Huegel writes, "These flowers are attractive nectar sources for a wide variety of pollinators." (8). Hummingbirds nectar at the flowers. (2). A butterfly attractant. Ants are often found within the flowers. 

NATIVE TO: Dr. Craig Huegel writes, "A common occurrence in salt marsh and freshwater wetland habitats throughout Florida and the Eastern Seaboard." (8). Most counties across Florida. "Coastal areas from MD to FL to TX to Cuba ." (2).
HABITAT: "Brackish marshes, coastal plains, swamps." (2). "Stream edges." (8). "Coastal interdunal swale, disturbed upland and wetland." (9).
LEGAL & CONSERVATION STATUS: "Least concern." (4, 5). Its IRC south Florida status is rated at "Secure." (9). 

SYNONYM:  Kosteletzkya virginica. "Synonym(s): Kosteletzkya althaeifolia, Kosteletzkya pentacarpos, Kosteletzkya smilacifolia, Kosteletzkya virginica var. althaeifolia, Kosteletzkya virginica var.aquilonia." (2).
DESCRIPTION: "A coarse, hairy (short-lived" perennial" (2) sub-shrub. "Virginia fen-rose or seashore mallow is much-branched and angular in habit." (2).
LIFE SPAN: "It only lives about 5 years." (2).
HEIGHT: "It grows 3-5 ft. tall and spreads to 4 ft. in width." (2). I have seen some plants grow to over 6' tall.
LEAVES: Alternate. "Elongated diamond-shaped leaves." (8).
FLOWERS: Bisexual. Two inches wide. "Pink, terminal or axillary, stalked flowers with yellow stamens." (2).
"Its leaves are triangular-ovate with triangular lobes at the base. The hibiscus-like flowers are light pink and 3 in. across with a central column of yellow stamens." (2). "Flowers close at night." (2).
FLOWERING SEASON: Mainly "June through October." (2). Blooms may begin to appear in "late spring." (8).
CULTURE:
LIGHT: Does best in full sun. Will flower in part shade.
SOIL pH: "Alkaline (pH>7.2) , Acidic (pH<6.8)." (2).
WATER: It "need wet soil to prosper." (8).
DROUGHT TOLERANCE: Low. (2) 
HEAT TOLERANCE: High. (2).
SALT TOLERANCE: "Moderately salt tolerant, though does best with high acidity." (2)
SOIL: "Prefers sand, but will tolerate clay." (2). "Seashore mallow adapts to less saline soils. The plant grows in brackish, swampy conditions, shallow standing water, or regular garden soil." (2).
PROPAGATION: "Seeds , Softwood Cuttings." (2). "Seeds germinate easily, particularly in warm (70 degree) soils. Wait for the capsule to turn brown and split open before collecting seed. Mature seeds are smooth and dark brown. Soak the night before planting. It may be necessary to dis-infest seeds of weevils before storing in sealed, refrigerated containers.: (2). "Tip cuttings, taken before flowering, will root." (2) 

NOTE: The Atlas of Florida Plants writes, "Populations in the Americas had been called K. virginica. Now the name K. pentacarpos is used since the American populations seem morphologically indistinguishable from the Eurasian populations (Blanchard 2008). Plants with narrower leaves (< 20 mm wide) with margins entire at the proximal half of the blade and reflexed lobes have been recognized as var. smilacifolia and endemic to peninsular Florida (Alexander et al. 2012), e.g. Jensen OS0563 (USF)."
RELATED SPECIES: There are an estimated 30 species in the genus. (10). There is just one other wild native Kosteletzkya here in Florida. It is the rare state-endangered, white flowered, Kosteletzkya depressa, the WHITE FENROSE. In Florida, it only grows in Miami-Dade and the mainland part of Monroe county.