PLATE 46—MYRIOPHYLLUM ROBUSTUM. 
Famiry HALORAGACE4.] [Genus MYRIOPHYLLUM, Linn. 
Myriophyllum robustum, Hook. f. Handb. N.Z. Fl. 67; Cheesem. Man. N.Z. Fl. 151. 
Myriophyllum robustum, which is by far the finest of the New Zealand species 
of the genus, was originally discovered by Mr. Colenso in some locality in the North 
Island, and has since been found in many lowland swamps or marshes from Ahipara 
and Mongonui southwards to Cook Strait. It is, however, far from being generally 
distributed, and is often absent from extensive areas apparently well adapted for 
it. Its chief centre of distribution is in the alluvial valleys of the Northern Wairoa, 
the Waikato, and the Thames Rivers; where, however, it is rapidly being destroyed 
either by the draining of the swamps or by the periodical burning of the vegetation 
therein. In these districts it can still be seen covering large stretches in swamps 
that are deeply covered with water in winter, but dry or nearly so in summer. 
Although occasionally seen in lakes or streams it is by no means either lacustrine 
or fluviatile to the same extent as its allies M. elatinoides and M. variefolium. In 
the South Island it appears to be rare, although it has been recorded as far south as 
Awatere on the east coast, and Hokitika on the west. 
M. robustum belongs to a section of the genus in which the whole of the leaves 
are verticillate and pectinately pinnatifid ; and is closely allied to the northern 
M. verticillatum, which ranges through a large portion of Europe, northern Asia, 
and North America. It can be distinguished from M. elatinoides and M. variefolium 
without the slightest difficulty by the much stouter and coarser habit, and by the 
upper leaves being verticillate as well as the lower. In addition to the above, the 
nuts are much larger and evidently tubercled. 
Prate 46. Myriophyllum robustum, drawn from specimens collected near Te Aroha, in the Thames 
Valley, and in the Waikato near Mercer. Fig. 1, hermaphrodite flower and leaf; 2, stamen ; 3, trans- 
verse section of ovary; 4, male flower; 5, section of male flower; 6, female flower; 7, transverse 
section of ovary ; 8, longitudinal section of ovary ; 9, fruit without tubercles ; 10, fruit with tubercles ; 
11, section of ripe carpel. (All enlarged.) 
