Observations on Muehlenbeckia Astoni and Its Seedlings.
[Read before the Manawatu Philosophical Society, 20th September, 1929; received by Editor, 27th May, 1930; issued separately, 23rd August, 1930.]
Muehlenbeckia Astoni Petrie, Trans. N.Z. Inst., 43 (1911), 257, t. 2, was described from specimens collected by Mr. B. C. Aston at Palliser Bay (Ruahine-Cook Botanical District), where it is of somewhat rare occurrence. The erect shrubby habit marks it off from the other New Zealand species of the genus. Petrie thus indicates the differentiae of the species: “This species is a near ally of M. complexa Meissn. The stout erect woody canelike shoots, the divaricate and interlacing habit of branching and the thin small obeordate-cuneate leaves clearly mark it off as distinct.” His material did not allow of full descriptions of the flowers and fruit. Similar plants were later collected by Mr. Aston on the Awatere River near Seddon, and by Dr. L. Cockayne near the mouth of the Flaxbourne Stream. Mr. W. Martin has recently found that the species is scattered through the north-eastern portion of the north-eastern South Island Botanical District. At Vernon, a little south of Blenheim, I have observed it growing as a member of an open shrubland community under dry conditions, in soil showing a mixture of clay and gravel. Associated plants are: Discaria toumatou, Hymenanthera dentata var. angustifolia, Muehlenbeckia australis, M. complexa (a low compact form). The present study is based on two selected adult plants (called here A and B), at Vernon. I am indebted to Mr. W. Martin and the late Mr. W. Purdie for photographs of these and their seedlings, and to Dr. H. H. Allan for assistance in preparing this paper for publication.
The two plants correspond in general to Petrie's description but afford supplementary details. Plant A (Pl. 39, Fig. 1), growing about 3 km. from the coast on a steep face of clay and gravel, is about 2.5 m. tall, and slightly more in spread. The diameter of the shoots at 60 cm. from the base averages 18 mm. (28 counts). Most shoots are straight and erect, but a few are zigzag and sloping; both forms terminate in masses of closely interlacing branchlets. An over-topping shoot frequently springs from below the terminal mass, and grows vertically. Leaves occur not only in fascicles, but also alternately along the elongated branchlets, the latter with elongated petioles. The petioles and leaf-margins are reddish brown. The flowers are pistillate, numerous, about 2.5 mm. diam., with a white, greenish or pinkish-green perianth, the edges incurved. There are eight staminodes, thick at their bases, pale green, with pinkish somewhat diversely shaped tips. The ovary is bluntly three-angled and three-grooved,
minutely rugulose, with three spreading fimbriate stigmas (Text-Fig. 1). The ripe nut is 2.2 mm. long, 1.2 mm. broad, three-angled, black or dark-brown, dull and rugulose, almost completely closed by the persistent perianth, which may be unaltered or succulent. All flowers appear to be pistillate, but their minute size and large number make it difficult to be certain that there are no functionally male flowers present, though such must be very few indeed. On male plants pistillate flowers have been occasionally observed. It is to be noted that several male plants of M. complexa grow nearby, while until the 1929 season the nearest male plant of M. Astoni was 140 m. away.
Fig. 2.—M. Astoni A. (a) Young branch; (b) Arrested branchlet; (c) Alternate leaves; (d) Fascicled leaves. M. Astoni B. (e) Alternate leaves; (f) Fascicled leaves.
Plant B (Pl. 39, Fig. 2) grows 90 m. nearer the coast on flat ground at the edge of a dry gravelly stream-bed, the top 30 cm. of soil being fine silt. It differs from A in having the leaves often variously laterally lobed (cf. Text-Fig. 2), fewer and larger flowers (about 3.3 mm. diam.), a larger nut, and the perianth more often enlarged and succulent. The diameter of the shoots at 60 cm. from the base averages 20 mm. (24 counts). A few fruits were gathered from both A and B at the end of April 1928, and sown immediately in separate tins. Germination was good, taking place in September (seven seedlings from A, and five from B). The plants were placed in their permanent beds in the winter of 1929.
Neither plant produced a uniform progeny, the seedlings falling into three groups. Group I. consists of a single plant, A 1 (cf. Pl. 40,Fig. 3). This has developed into a stunted, much and compactly branched plant with stout puberulous branchlets, dark greyish brown
stems, subcordate leaves with retuse apices and somewhat lobed margins, the petioles being about 9 mm. long. It has proved to be slightly deciduous in winter, and has as yet shown no sign of flowering. This plant is strongly suggestive of M. complexa influence.
Group II. is made up of seedlings from both A and B—A2 to A7, B1, B5. These eight plants, though showing individual differences, have several important characteristics in common, and present a strong M. Astoni facies (Plates 40, 41). They have developed into erect spreading shrubs, with slender, flexuous, glabrous, more or less divaricating branchlets, with reddish-brown bark. The leaves are cuneate or rounded at their bases, with retuse apices and lobed or unlobed margins, on petioles about 20 mm. long. All were deciduous in winter. During September-October 1929 all developed from their bases one or more stout, erect, straight shoots of rapid growth. By March 1930 this group presented the appearance of miniature M. Astoni plants, all except A2 showing very vigorous growth. A3, A4, B1, B5 bore at this time a few staminate flowers.
Group III. is made up of seedlings B2, B3, B4, and is markedly distinct from group II. These plants are of prostrate or semiprostrate (B4) sprawling habit (Pl. 41, Fig. 4). The branchlets are very long, flexuous, puberulous, greyish-brown (B2) or dark-brown. The leaves are subeordate, obtuse to somewhate retuse at the apices (or in young leaves somewhat apiculate), lobed (very slightly so in B3) on the margins, with petioles about 12 mm. long. The plants are of vigorous growth, deciduous to a considerable extent in winter. B2 in March 1930 bore a few staminate flowers, which were larger than those in group II. There was thus in this group a marked approach to M. complexa. Both in group II. and group III. the leaves showed a good deal of polymorphy (Text-Fig. 3).
The features shown by the 12 seedlings suggest the following possibilities:—
(1) M. Astoni may pass through a distinct juvenile form, as is known to occur in some other species of the genus. (2) Hybridization has occurred with M. complexa, and perhaps with M. australis. (3) The parent plants may themselves be hybrids, their seedlings showing segregation. It is unlikely that epharmony has played much part, as the seedlings were grown under conditions as similar as possible to those of the parents. The matter can be definitely decided only by experiment, but the indications appear to be that M. Astoni does pass through a juvenile form. The character of the fruits, unlike those of any other New Zealand species, speaks for the specific distinctness of M. Astoni. The seedlings of group III., especially, strongly suggest, however, that M. Astoni has hybridized with M. Complexa. Again, the frequent lobing of the leaves in the adult B, its fewer larger flowers and fruits, suggest that this plant may itself be a hybrid segregate very close to M. Astoni. It is hoped to throw further light on the problems by controlled pollinations.