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The native aquatic plants of New Zealand can be grouped in to six different life forms. The mosses and liverworts found in New Zealand are mostly cosmopolitan and are best suited to specialist tanks. Charophytes (macroalgae of the genera Chara and Nitella) are also cosmopolitan. A number of charophytes are desirable in that they provide refuge for juvenile fish, they help condition the water and can be very attractive with their distinctive growth forms and appearance. Delicate compact charophyte species can make an attractive foreground in an aquarium. Of the tall growing submersed species, New Zealand has few endemic milfoils and pondweeds and those with greatest potential are illustrated and discussed. The most interesting and diverse group of water plants are those that form turfs. New Zealand has a wide diversity of turf species with different leaf shapes and growth habits. Spread is usually by rhizomes and given good light conditions they can form a vigorous compact carpet across the base of an aquarium or pond. One internationally well known, but incorrectly named example is Lilaeopsis novae-zelandiae. The New Zealand native Isoetes can provide an ideal foreground plant in aquariums.
New Zealand has no native water lilies, while the only free-floating species are universally common. A wide variety of small to large native emergent species are found around the margin of waterbodies. Some are grown for ornamental ponds while others are used in wetlands designed to treat or purify waste water.
Issues relating to the collection, culture and marketing of aquatic plants have particular relevance to their suitability in the aquarium trade. The question of what makes a good aquarium plant is considered, including why exotic plant species are so successful and still provide the bulk of the aquarium and pond market both in New Zealand and internationally. More screening, culture trials and market evaluation is required on selected species.
New Zealand was predominantly forested until the 1800s and of the different kinds of flowering vegetation and ferns belonging to the pre-European vegetation, around three-quarters are endemic. These include many that are prized as garden shrubs and for alpine or herbaceous gardens (e.g. evergreen veronicas - Hebe, Nikau palms - Rhopalostylis, New Zealand flax - Phormium, tussock grasses, daisy bushes - Oleraia).
With the advent of European colonisation in the late 1800s and the subsequent extensive agricultural development, large areas of land were cleared of native vegetation and over 90% of the original wetlands are now drained for farming. Associated outcomes of agricultural development include erosion due to deforestation, which combined with increased run-off of nutrients, has led to nutrient enrichment and siltation of many smaller waterbodies in particular.
Another post-European impact has been the extensive introduction of adventive plants and animals. New Zealand had no native mammals (with the exception of two flying bats) and now in addition to numerous farmed animals there are also many wild possums, rabbits, deer, goats and pigs which continue to damage and even destroy native vegetation throughout the country. By 1940 about 500 alien plant species had become established and these too have had a marked impact on the native vegetation. Apart from exotic forestry, invasive spread of uncontrolled alien species has become a major management issue. Within natural waterbodies, the influence of land management practices within catchments along with the effect of invasive exotic species has resulted in few waterbodies retaining the natural or original indigenous aquatic vegetation, apart from those still isolated from human influence.
The international search for potential new aquarium plants and the geographical isolation of New Zealand has generated overseas interest in our indigenous aquatic plant species. Fortunately, isolated and protected areas still remain, so that it has still been possible to identify and retrieve most of our original aquatic plant species. Many large clear-water lakes have been protected by their vast size, under-developed catchments and reserve status (e.g. National Parks), while small isolated lakes with limited or no public access often still retain the original aquatic vegetation.
Interest in our indigenous aquatic species and a national desire to minimise use of potentially invasive exotic species in the New Zealand aquarium trade, prompted a research screening programme to identify which if any of our native species may be suitable for aquarium and pond use. This illustrated paper discusses a range of different plants, looks at their growth habit in the natural environment and considers their potential use in aquaria and ponds.
Research to identify the potential suitability of New Zealand native aquatic plants for use in aquaria began with the view of providing safe alternatives to a range of species regarded as undesirable or of significant weed potential. Legislation in New Zealand prohibits the sale and distribution of a certain aquarium and pond plant species (e.g. elodea densa [i.e. Egeria densa], elodea crispa [Lagarosiphon major], hornwort [Ceratophyllum demersum], water hyacinth and salvinia). Furthermore, there are restrictions on the importation of a range of aquarium and pond plants, while others that are not specified as approved or prohibited species can only be imported after a permit has been granted, followed by certification verifying disease and pest free growth while under quarantine, plus an acceptable "risk assessment" evaluation carried out at the importer's expense.
Of the few native moss species tested, only Hypnodendron marginatum grew well under all test conditions. Many other mosses occur in New Zealand and one endangered species (Fissidens berteroi) is undergoing further study with a view to identifying its ecological requirements to ensure future protection or culture. There are many moss genera around the world and the genus Fissidens alone has over 900 species alone, but like many other genera, only a few species are truly aquatic. Aquatic moss species are often poorly documented and further study will be required on this diverse group of plants. There is little advantage in considering any of the New Zealand species further at this stage when there are already well established tropical mosses (e.g. Java Moss or Vesicularia dubyana which prefers temperatures exceeding 23C or 73F) and cold water mosses (e.g. Fontinalis antipyretica up to 20C or 68F maximum) available for aquarists. Furthermore there are many other cosmopolitan mosses (eg. species of Drepanocladus, Amblystegium and Fontinalis as well as other genera) which have aquatic forms and can be grown successfully in aquaria.
Compared to the mosses there are very few truly aquatic liverworts. Of the deep water New Zealand specimens, none are likely to be suitable on account of their very slow growth rate. There are only two well known and cosmopolitan liverworts grown as free floating tank covers. Riccia fluitans (commonly called Crystalwort) is a popular aquarium plant, while the other liverwort Ricciocarpus natans is seldom used. Both species are native to New Zealand.
Many books on aquarium plants fail to even mention this attractive group of plants, while those that do often include only one or two species of Nitella. Undoubtedly one of the reasons is that some species are too delicate for general purpose use in tanks while others may be readily eaten or disturbed by a variety fish. Nevertheless, some species can form excellent robust growths and Nitella flexilis, which can tolerate temperatures up to 28C is most commonly sited . Species with an open branching growth habit can be suitable for juvenile fish, while delicate compact species can make an attractive foreground in a tank.
Nearly all species in New Zealand are cosmopolitan. Four species of Chara and six species of Nitella are commonly found natives in New Zealand, although only Nitella hookerii is endemic. N. hookerii is a fast growing, fine, highly branched plant which is easy to propagate. It may occasionally require control in some waterbodies, including in aquaria and tanks. These properties can make this plant ideal for spawning fish and as a refuge for small fish. Perhaps the most attractive of the native Nitella species investigated, include N. leptostachys, N. pseudoflabellata and N. hyalina. These are slower growing and more compact in growth habit. Three Chara species which are particularly attractive are Chara fibrosa, C. corallina and C. globularis. The first two species are unreliable and too difficult to grow in aquaria, but they can be grown in outdoor ponds successfully. C. globularis on the other hand is relatively hardy, can tolerate higher temperatures (up to 24C) than the other charophytes and with its attractive emerald green colour, it makes an attractive backdrop to an aquarium. The growth of charophytes in warm water aquariums generally deteriorated when temperatures exceeded 20C. Most of the charophytes can be propagated from vegetative material, however, the potential to grow Chara vulgaris (a species that is widespread in many countries but is not present in New Zealand) and Nitella pseudoflabellata (a New Zealand native) from seed (oospores) requires further investigation as this may well overcome some of the difficulties in collecting, transporting and establishing easily damaged specimens. Unfortunately most of these species appear to be better suited to cold water aquariums and outdoor ponds, provided they are not exposed to feeding pressure or damage by larger fish such as goldfish.
Milfoils are mostly cosmopolitan, with around 40 species. Many of the milfoils originate from temperate climates in the Southern Hemisphere and USA and their low tolerance to warm water aquaria can result in poor growth and loss of submerged leaves. Some of these species may well be suitable for aquaria and ponds, but interest in obtaining new milfoil species has been reported as somewhat limited since most species tend to look alike . Milfoils that have become established in the aquarium trade include Myriophyllum hippuroides and M. verticillatum, both of which tolerate water temperatures up to 23C, while outdoor ponds are generally considered a more suitable option for milfoils such as M. aquaticum (i.e. parrot's feather which may still be referred to by its old name M. brasiliense) that tend to quickly form emergent foliage under cultivation.
Of the New Zealand native milfoils , only two are endemic (M. robustum and M. triphyllum). M. robustum is an uncommon species and is classified as vulnerable in terms of its future survival . It is bronze coloured and can be cultivated to produce large submersed and robust emergent leaves. Unfortunately it is rather similar to M. aquaticum (parrot's feather) in appearance and its preference for acid or peat bog habitats is likely to limit its usefulness for future commercial cultivation and also exclude its use in alkaline water or concrete lined pools. M. triphyllum (previously thought to be the same as M. elatinoides) is too difficult to cultivate and performs poorly in aquaria. M. propinquum, a native species which is also found in Australia, may be suitable for tropical aquaria (upper temperature tolerance appears to be around 23C and it is already a popular plant for use in ornamental outdoor ponds in New Zealand. This plant can be grown hydroponically since it is heterophyllous and the small aerial leaves quickly revert to an underwater growth form on submergence in ponds or aquaria. Alternatively the plants can continue to grow as prostrate mats on damp pool margins.
Other plants that belong to this life form include species of Ruppia (horse's mane weed), Zannichellia and Lepilaena. These genera are found around the world, but all have fine hair-like leaves and none have become recognised as worthwhile aquarium specimens . Species of these genera that are endemic to New Zealand have no distinguishing characteristics that would recommend them for further investigation.
The largest and most distinguished member of this group is Isoetes (Quillwort), which can form a compact turf to 6 metres in clear water lakes in New Zealand. This is an ideal midground plant in aquariums, but no runners are produced so plants must be individually planted. Isoetes lacustris and the larger I. malinverniana are often noted in aquarium literature, but there often appears to be a shortage of supply on account of the continuing decline in their natural occurrence, and from difficulties experienced with the culture of these plants. Although propagation by spores has been suggested , it has also been recommended "that one should be satisfied with collecting these plants under natural conditions and letting them stand without multiplying in aquaria" . The Isoetes species noted in the aquarium literature are reported to have a limited temperature tolerance with culture recommended to be between 18-22C. Trials with the New Zealand Isoetes suggest a greater temperature tolerance with successful culture in cold water (10C) and warm water up to 24C. There appears to be three varieties of one genus (I. kirkii) in New Zealand  and further study of their taxonomy and potential use in aquaria is recommended. One growth form collected from a southern lake grows very tall blades up to 0.5-1m long (similar in appearance to I. malinverniana). This growth habit continues even in aquaria, with the result that leaves grow across the surface. The more common shorter variety (10-30cm) can be collected from the many abundant natural sources and grown under appropriate culture conditions so as to produce robust specimens with up to 40 leaves, before being transplanted into aquaria. There is considerable potential for large scale culture of this species to form large many-leaved plants, either from spore material or by using the typically small statured plants from natural field populations.
A particularly interesting native buttercup (also found in Australia) is the non-weedy Ranunculus amphitrichus (waoriki). This plant has palmate, non-hairy leaves, can be readily grown as an emergent plant but will adapt to submergence within an aquarium even in warm water up to 24C. Worldwide there are approximately 35 species of Ranunculus that are aquatic and other potentially useful aquarium species are likely to exist, but of the New Zealand species R. amphitrichus appears to have the greatest potential and the most suitable growth characteristics.
There are many other New Zealand species of this low growing turf forming nature, but unfortunately there is often little if any notable difference in appearance to their counterparts from other countries and their use as aquarium plants is probably not worth investigating further. For example, Eleocharis pusilla looks like E. acicularis (hair grass), but it is less robust and is unable to grow in warm water conditions. Pilularia novae-zelandiae (Pillwort) is an uncommon and unusual fern with distinctive concentric coiling of its terminal, hair-like fronds, but it is largely indistinguishable form the popular and readily cultivated P. glogulifera. There are also a number of endemic and native Hydrocotyle species (Pennyworts) in New Zealand that have never been tested for their suitability in aquaria, however the presence of the well established, cold and warm water tolerant H. vulgaris (Pennywort or Umbrella plant) within the aquarium trade, reduces the value in exploring this group any further.
A wide variety of small to large native and endemic emergent species are found around the margin of waterbodies or grow within the waters edge. Species of Schoenoplectus, Eleocharis, Baumea, Cyperus, Typha and Juncus are common. Many of the genera in this group are cosmopolitan and are well known by pond plant growers and nursery suppliers. Some species are cultivated specifically for ornamental ponds while others have been used in wetlands designed to treat or purify waste water.
A number of issues were identified during the study of potential native aquarium species for the New Zealand market:
Commercial culture within New Zealand may also be an option, particularly if the additional international demand is sufficient to justify their culture so that promotion of these species on to the local market becomes economical. New Zealand culture also has the advantage that all of the native species discussed are temperate plants which are well suited to New Zealand climatic conditions, as well as the renowned favourable growing conditions in this country which are conducive to excellent plant growth. Interest from European countries in potential culture of aquarium plants in New Zealand for international supply has arisen, since significant savings in plant culture may be achieved through savings in the reduced need for supplementary heating and lighting.
Alternative approaches should also be considered. For example, the potential large scale culture of Isoetes from spores should be investigated further, while the option of nuturing wild sourced plants by providing specialised culture conditions prior to marketing, may well be economically preferable. Species that can be grown hydroponically out of water probably provide the best potential for commercial culture, while true aquatics that can only be grown under water are often slower to grow and more demanding of space. Such plants may well be better sourced from natural populations, provided there are adequate and sustainable sources.
Finally, one interesting question still to consider is why exotic plant species are so successful and still provide the bulk of the aquarium and pond market both in New Zealand and internationally. Inevitably, the bulk of the aquarium trade is based primarily on tropical and sub-tropical fish species which are well renowned for their diversity of size, colour and form. This has a direct bearing on the type of plants which are best suited to growth in these conditions. Aquatic plants of tropical origin are naturally suited to tropical aquaria, while the range of temperate aquatic species able to tolerate tropical aquaria is somewhat restricted. Insufficient research or knowledge on potential alternative plants, popular aquarium books based largely on tropical species and the proven ease of culture and performance of the existing range of commercially available species, have all contributed to the market domination by existing species.
Cold water aquaria and outdoor ponds tend to be based on different fish and often include alternative plant species. In this regard it is interesting to note that some sub-tropical water plant species have been highly successful in their global distribution and vigorous growth even in temperate climates. For example, various species of Oxygen Weed (such as elodea densa [Egeria densa] and hornwort [Ceratophyllum demersum])) have recently come to dominate many New Zealand waterways. Their abundant and healthy growth have proven ideal for use in cold water aquaria and outdoor ponds both in New Zealand and in other countries. In fact it was from initially imported plants used within this sector of the trade that led to many of the current populations which have developed from escaped or deliberately released plants entering in to natural waterbodies. Their hardy nature, resistance to fish browsing, ease of propagation and adaptability to indoor aquaria or outdoor ponds have been largely responsible for their adoption by commercial plant suppliers for cold water aquaria and the pond plant trade. Ironically, New Zealand has now become a significant supplier of these same exotic species on to the international market. Their abundance and exceptional quality from natural populations avoids costs associated with their culture and at the same time New Zealand can meet any shortage of supply within the Northern Hemisphere when their spring demand escalates.
More screening, culture trials and market evaluation is recommended on those New Zealand native species discussed in this paper. The challenge beyond this is to identify those species that have qualities comparable to or even better than those species already established within the aquarium trade and then to develop their market potential accordingly.
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