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2. Nasturtium R.Br. (Cruciferae)
The common watercress (Nasturtium officinale R.Br. [sensu lato]) was first recorded from New Zealand by Hooker (1852: 14) when he noted “…. appears to be naturalized about Auckland,…,” and the distribution was widened by the same author (1864A 10) with the observation “…. abundantly naturalized in rivers, etc.” and further (1864A: 15) “…. a pest in the rivers about Canterbury “The through establishment of the species, at least locally, in these early years, is evidenced by Hooker's statement (1864B 124) that it cost more than £300 per annum to clear this weed in the Avon River, Christchurch. This local abundance may have prompted the colonists to introduce the Australian black swan in an attempt to control the weed, as is stated by Murphy (1951. 577), who reports that bird as “introduced at the behest of sportsmen or, as some New Zealanders allege, for the purpose of destroying the introduced watercress”
Field observations and later examination of herbarium material showed two distinct entities in our concept of N. officinale R. Br., one being N. officinale [sensu stricto], the other* * N. microphyllum Boenn. ex Rchb.
The two species are readily distinguished on macroscopic fruit characters—N. officinale the siliquae are relatively short and broad, pedicels stout, the seeds arranged in two distinct rows, and in N. microphyllum the siliquae are long and slender, often arcuate, the pedicels longer and more slender, and the seeds in one, or indistinctly two-rowed. The sculpturing of the seed coat is diagnostic—in N. officinale there are about 25 large depressions on each face, and in N. microphyllum about 100 small depressions on each face. Aside from the fruit
[Footnote] * Species recorded for first time for New Zealand.
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and seed characters, the position of the mature anthers differs—in N. officinale that anthers are introrse, and in N. microphyllum the anthers are extrorse.
Overseas, the two species are distinct in autumn aspect—the stems and leaves of N. officinale remain green in autumn, while the stems and leaves of N. microphyllum turn purple-brown in autumn. I have been unable to examine the autumn aspect of N. officinale in New Zealand, but all stands of N. microphyllum examined show the characteristic purplish-brown autumn colour.
Further collections are required to provide more accurate data on distribution, but on the basis of field observations and herbarium material examined, N. officinale appears to be restricted to the North Island, while N. microphyllum occurs in both Islands, locally common in localities from the Manawatu and Wairarapa districts southwards.
Specimens examined:—
A. Nasturtium microphyllum Boenn. ex Rchb.
Auckland Institute and Museum, Auckland: Auckland, T. F. Cheeseman, date not stated (28731, 28732, 28733). Botany Division, D.S.I.R., Wellington: Feilding, V. D. Zotov, 1928 (707, 708); Foxton Line, Manawatu, I. W. Davey, 1937 (18293); Tauherenikau, Wairarapa, V. D. Zotov, 1947 (59087); Wilton's Bush, Wellington, R. Mason, 1950 (70339); Waiwhetu Stream, Lower Hutt, R. Mason, 1950 (65623); Nelson, D. M. E. Merry, 1952 (81416); Wakefield, Nelson. W. O. Sly, 1952 (81415); north of Birchfield, Buller County, R. Mason and N. T. Moar, (81040, 81217); north of Charleston, Buller County, R. Mason and N. T. Moar, 1953 (81291); Cass, Canterbury, R. Mason, 1951 (71455); Lakeside, Leeston, P. R. Barrer, 1952 (81414); Washdyke, W. J. Kissock, 1952 (81418), Pleasant Point, W. J. Kissock, 1952 (81417); Invercargill, A. L. Poole, 1940 (23931, 29470). Dominion Museum, Wellington T. Kirk, 1893.
B. N. officinale R.Br.
Auckland Institute and Museum, Auckland: Taipa, North Auckland, R. Cooper, 1950 (36049). Botany Division, D.S.I.R., Wellington: Thompson's Lake, South Head, Manakau Harbour, N T. Moar, 1950 (70875); Whakataki River, Wairarapa, V. D. Zotov, 1945 (48680); Hutt River, near Upper Hutt, 1950 (81424, 81425); Cape Turakirae, R. Mason, 1952 (74081); near Barney's Hut, Palliser Bay, R. Mason, 1952 (74087). Represented in Seed Herbarium by two collections: Plant Research Station farm near Palmerston North, collector not stated, 1927; Orongorongo River, R. Mason, 1946.
A collection by Miss R. Mason from Ohariu Valley, Wellington Province (81586) appears to be one of the hybrid forms between the two species, but does not show the extreme sterility associated with overseas material. A series of specimens collected by my wife from Pakowhai, Hawke's Bay (81420, 81421, 81422, 81423) have siliquae longer and narrower than typical N. officinale, the seed testa depressions range between 40 and 50, and the seeds are arranged in two rows. Again in this material, there are less than 25 per cent of sterile ovules per fruit.