Isolepis fluitans subsp. fluitans. Photographer: Jeremy Rolfe.Freshwater aquatic plants (also called macrophytes or hydrophytes) are those that have adapted to living in or on aquatic environments. Aquatic plants are an ecological rather than a taxonomic group and include obligate and facultative (or amphibious) species, representing a range of life forms; submerged, free-floating, floating-leaved, erect emergent and sprawling emergent. Aquatic plants are considered distinct from marine algae or seaweeds.
Unlike New Zealand’s terrestrial flora, 66% of our indigenous freshwater flora are common with Australia (Champion and Clayton 2000). In a similar way Chatham (Rekohu) Island has a subset of the New Zealand freshwater flora, with 32% of New Zealand macrophytes present (Champion and Clayton 2004). These natural introductions are presumably the result of seed transfer by migratory waterfowl or wind dispersal.
Mud pondweed (Potamogeton suboblongus). Photos: Jeremy Rolfe
Common milfoil (Myriophyllum propinquum). Photo: Jeremy Rolfe
Trithuria inconspicua. Photo by Jeremy Rolfe.There is a diverse range of taxonomic groups comprising aquatic plants including; charophytes (specialised algae resembling higher plants with
1 family, 4 genera, 18 species), fern allies (1 family, 1 genus, 2 species), ferns (2 families, 3 genera, 4 species), proto angiosperms (3 families, 4 genera, 5 species), monocotyledons (14 families, 24 genera, 35 species) and dicotyledons (15 families, 26 genera, 53 species). Thus a wide range of taxonomically unrelated species have colonised aquatic habitats, often with only one or a few species representing an individual family which has a much greater number of terrestrial representatives. The largest genera are Nitella (11 indigenous, including at least 3 endemic species), Myriophyllum (6 indigenous including 3 endemic, 1 alien species), Potamogeton (4 indigenous including 2 endemic, 2 alien species) Chara (4 indigenous including 1 probable endemic, 1 alien species), and Ranunculus (4 indigenous including 2 endemic, 1 alien species).
For more information see*
- Champion, P.D.; Clayton, J.S. (2000). Border Control for potential aquatic weeds. Stage 1. Weed risk model. Science for Conservation 141.
- Champion, P.D.; Clayton, J.S. (2004). Aquatic vegetation of Chatham Island (Rekohu). DOC Science Internal Series 164.
- Coffey, B.T.; Clayton, J.S. (1988). New Zealand Water Plants: A guide to plants found in New Zealand freshwaters. Ruakura Agriculture Centre, Hamilton.
- Johnson, P.N.; Brooke, P.A. (1998). Wetland plants in New Zealand. Manaaki Whenua Press, Lincoln.
- Free aquatic plant information from NIWA (National Institute of water and Atmospheric Research)