Plant problems

Why Are My Puccinellia Leaves Curling?

Q: How do I identify puccinellia maritima and puccinellia distans?

Puccinellia maritima (common saltmarsh grass) and Puccinellia distans (reflexed saltmarsh grass) are two of the most commonly encountered UK Puccinellia species and can be distinguished by habitat and by the character of their flower panicle; both are perennial, tufted or mat-forming grasses with narrow, in-rolled or flat, grey-green to glaucous, tough, and often slightly fleshy-textured leaves that reflect their halophyte adaptation. Puccinellia maritima: habitat is coastal saltmarsh, almost always on tidal saltmarsh in the tidal zone; the panicle branches are erect to spreading at anthesis (when in flower) but typically become somewhat reflexed (spreading downward) after flowering; the spikelets are oblong to narrowly oblong, typically 4 to 10 mm long; one of the dominant grasses of the lower to mid-saltmarsh; creeping, mat-forming habit; very common on all UK estuaries and coastal inlets. Puccinellia distans: habitat is upper saltmarsh, coastal disturbed ground, and characteristically inland road verges and motorway central reservations with elevated soil salinity from de-icing salt; the key identification feature is the characteristic reflexing (spreading strongly downward) of the panicle branches, which become very strongly reflexed and spread outward and downward at right angles to the panicle axis after anthesis; this strongly reflexed, spreading panicle is the most readily observed field character for P. distans; the spikelets are smaller (2.5 to 6 mm); more upright growth habit than P. maritima; inland road verge occurrence is diagnostic for P. distans. The two species hybridise where they grow together; the hybrid Puccinellia x hybrida is occasionally recorded at coastal sites.

Puccinellia maritima (common saltmarsh grass) is the dominant pioneer and mat-forming grass of UK coastal saltmarsh, one of the most ecologically important plants in the UK coastal ecosystem. Puccinellia distans (reflexed saltmarsh grass) is found on coastal saltmarsh and, distinctively, on inland road verges salinised by de-icing salt. Leaves curl from drought and drying between tidal floods, hypersaline stress in hot weather, or winter frost damage.

Drought between tidal floods

In an unusually dry UK summer, the upper and drier parts of the saltmarsh can experience drought stress between high tide inundations; the creek levees and landward saltmarsh margins are most susceptible; the already somewhat in-rolled leaves curl more tightly and the leaf tips yellow. Puccinellia distans on a road verge, lacking the regular wetting of the tide, is more vulnerable to drought stress than P. maritima on an active tidal saltmarsh.

What to do

In a natural saltmarsh, no intervention is needed; the tidal cycle and natural rainfall maintain the plant; extended drought is a weather event the plant recovers from in normal UK conditions with the next substantial rain and tidal inundation. Puccinellia distans on a saline road verge or a garden salt bed requires no supplemental watering in UK conditions; the plant is adapted to periodic drought stress in its saline roadside habitat.

Hypersaline stress in hot weather

In a hot, dry UK summer, evaporation from the saltmarsh surface can raise soil salt concentration in the upper horizon well above typical seawater levels between tidal floods; these hypersaline conditions cause osmotic stress even in Puccinellia, triggering tighter leaf rolling and leaf tip yellowing and browning. Most pronounced in the upper, less frequently flooded saltmarsh and in impounded or reclaimed saltmarsh where tidal flushing is reduced.

What to do

No management action is appropriate or effective in a natural saltmarsh; hypersaline surface stress is a natural and periodic feature of the saltmarsh environment and Puccinellia maritima is adapted to it; the plant recovers with the next tidal inundation that lowers surface salinity back toward normal levels. At impounded or managed coastal sites where tidal flushing has been reduced or eliminated, restoring tidal exchange is the most effective long-term action to prevent chronic hypersaline stress.

Winter frost damage

The persistent mat of Puccinellia maritima can suffer leaf tip yellowing and die-back in a severe UK winter; the plant loses its characteristic dense, bright green colour. However, it recovers strongly from winter damage as temperatures rise in spring, growing from the persistent creeping base. Puccinellia distans on inland road verges is actually exposed to more road salt in winter (when de-icing occurs) and is less frost-stressed than during summer drought.

What to do

No intervention is needed for winter frost damage on natural saltmarsh; the plant recovers from frost damage in spring without management. The naturally salt-rich conditions of the saltmarsh provide some frost protection through freezing-point depression of the soil solution, and UK saltmarsh Puccinellia populations have long experience of UK winter conditions.

Frequently asked questions

Why are my puccinellia leaves curling?

Puccinellia leaves curl most commonly because of drought between tidal floods (upper saltmarsh and creek levees most susceptible; leaves curl more tightly between inundations in dry weather; no intervention needed in natural saltmarsh; P. distans on road verges is more drought-vulnerable than tidal P. maritima), hypersaline stress in hot weather (evaporation raises soil salt above seawater levels between floods; osmotic stress even in this halophyte; tighter leaf rolling and tip yellowing; no management action appropriate in natural saltmarsh; restoring tidal exchange helps in impounded sites), or winter frost damage (leaf tip yellowing and die-back in severe winters; plant recovers strongly from creeping base in spring; salt in soil solution provides some frost protection; no intervention needed). Zero-maintenance in the correct tidal or saline-road habitat.

What is the ecological importance of puccinellia maritima on UK saltmarshes?

The single most ecologically important grass in UK coastal saltmarsh and one of the most important plants in the entire UK coastal ecosystem. Pioneer and engineer: dominant pioneer grass of the lower saltmarsh; colonises open mudflat by vegetative spread; traps suspended sediment from tidal water; builds the saltmarsh platform that supports the diverse upper saltmarsh community. Wave energy dissipation and flood defence: the dense flexible mat dissipates wave energy; the vegetated saltmarsh platform significantly reduces coastal flood risk; Environment Agency flood defence strategies increasingly recognise Puccinellia saltmarsh as cost-effective nature-based coastal defence. Blue carbon: saltmarshes are among the most carbon-dense ecosystems on Earth; P. maritima-dominated lower saltmarsh contributes to blue carbon storage through plant biomass and organic carbon in trapped sediment. Invertebrate and bird habitat: the Puccinellia mat provides foraging habitat for dunlin, redshank, curlew, and black-tailed godwit and supports specialist saltmarsh invertebrates.

Why is puccinellia distans found on UK roadsides and motorways?

A direct consequence of sodium chloride road de-icing since the 1960s and 1970s. Road salt dissolves in rain and meltwater and is washed into adjacent road verge soil; repeated winter applications have created a zone of persistently elevated soil salinity along UK road margins toxic to most native plants but hospitable to salt-tolerant specialists. Dispersal: windblown from coastal sites; mud on vehicle tyres; contaminated road salt or road-building material from coastal deposits. The combination of elevated soil salinity, drought stress in freely draining road verge soil, and periodic disturbance mimics upper saltmarsh; Puccinellia distans is perfectly adapted to these conditions. Now widespread on lowland England road verges, particularly Midlands; present on A1, M1, M6, M40, M4, and other major UK roads.

How do I identify puccinellia maritima and puccinellia distans?

Both: perennial; narrow, in-rolled or flat, grey-green to glaucous, tough, slightly fleshy-textured leaves; tufted or mat-forming. P. maritima: coastal tidal saltmarsh only; panicle branches erect to spreading at anthesis, somewhat reflexed after flowering; spikelets 4 to 10 mm; dominant mat-forming lower to mid-saltmarsh grass; creeping habit; very common on all UK estuaries. P. distans: coastal upper saltmarsh and characteristically inland road verges salinised by de-icing salt; key field character: panicle branches become very strongly reflexed (spreading strongly downward) after anthesis — the most readily observed field character; spikelets smaller (2.5 to 6 mm); more upright growth habit; inland road verge occurrence is diagnostic. Hybridise at coastal contact zones; hybrid P. x hybrida occasionally recorded.