The river's tendency to flood has enabled it to retain its wild character, even in the wide arable lands around Rethel. Its banks are home to some rare and unique species, evidence of the flora and fauna of Antiquity. Plant varieties rarely found in Champagne-Ardenne have been recorded in the valley and more than a dozen have been given heritage status and protected at regional level. These include Gratiola officinalis (hedge hyssop), water soldier, and water germander. Not far from Acy-Romance, the steep slopes of the Monts de Sery, a natural hill rising to 173 metres above the plain, are home to a rich variety of flora. 

On the chalk plain, the dry grassland, known locally as savart, the last remaining evidence of the ancient grazing meadows, is disappearing. Over 160 plant species characteristic of the local chalk grasslands have been recorded there, including some fifteen different orchids. Only small patches of the ancient chalk grasslands now remain, isolated areas unsuitable for modern farming techniques or inside the boundary fences of the Marne's huge military camps. Cassini's historic map of France shows very few woodland areas around Rethel and Porcien. The Ardennes forest has been exploited for centuries, and during the 1800s its Norway spruce and Scots pine were a commercially valuable source of resin. It bears little resemblance to the ancient woodlands that once stood there. Oak, beech and hornbeam are light-loving species which grew in the Jurassic landscape of the pre-Ardennes hilltops, on the upper valley terraces and in Argonne. Hazel and crab apple trees can be found on the embankments near the river.

The contribution of archaeology

Palynological and anthracological studies, complementary branches of archaeology, show an largely anthropised environment, marked by the actions of man. Fields were cultivated in the immediate area of the settlement. The pollen found shows a mosaic of combinations of mainly local plants: cereals and Plantago lanceolata (plantain); ruderal species: chenopodiaceae, caryophyllaceae; grassland species: ombelliferae, gramineae. Oak, elder, pine, lime and hazel are all represented. As well as these principal species, the wood charcoal found shows evidence of cherry, willow, elm, apple and spindle trees. 

Chalky soils are unsuitable for the wood species generally used for carpentry, principally oak and beech. The robustness of some of the buildings in the village of Acy-Romance implies the importation of some huge tree trunks (sawn beams 80 cm a side) from the valley and probably from the pre-Ardennes hills. Floating, or the transport of timber by water, could have been a useful means of transport at certain times of the year, although the density of green wood makes this technique problematic.