Tuatara: Volume 30, Issue 1, December 1988
Cone and Seed Phenology in Several New Zealand Conifer Tree Species
Cone and Seed Phenology in Several New Zealand Conifer Tree Species
The stages of development of male cones, ovules and seeds in six New Zealand coniferous trees are described and illustrated. In kahikatea (Dacrycarpus dacrydioides), totara (Podocarpus totara), Hall's totara (P. hallii) and tanekaha (Phyllocladus trichomanoides) the visible stages are completed in one growing season, fertilisation occurring about 6 or 8 weeks after pollination. In miro (Prumnopitys ferruginea) and matai (P. taxifolia) the visible stages of ovule and seed development occupy two growing seasons and fertilisation occurs 12 months or more after pollination.
Key words: Podocarpaceae, Podocarpus, Dacrycarpus, Prumnopitys, Dacrydium, Phyllocladus, conifer. seed, ovule, male cone, phenology.
There are distinct differences in the reproductive structures and in the timing of the sequence of events which leads to the production of ripe seed in six of New Zealand's tall forest coniferous trees. In this article the development of male cones and female ovules in kahikatea (Dacrycarpus dacrydioides), true totara (Podocarpus totara), Hall's totara (P. hallii), miro (Prumnopitys ferruginea), matai (P. taxifolia) and tanekaha (Phyllocladus trichomanoides) will be described. The development of these structures in rimu (Dacrydium cupressinum) has already been described (McEwen, 1983).
The ovule-bearing structures of podocarp trees are modified, reduced female cones. In matai, in particular, the structure resembles a minute enlongated cone with several ovules borne spirally on a cone stalk, each in the axil of a bract scale or carpidium.
In the Coniferales there are two types of reproductive cycles, a short and a long type, and both are represented among these New Zealand tree species. In the short type the whole reproductive cycle occupies approximately one year and the time between pollination and fertilisation is only 6 or 8 weeks; whereas in the long type the cycle occupies two years and the time between pollination and fertilisation is 12 months or more. The long reproductive cycle also occurs in rimu (Dacrydium cupressinum) (McEwen, 1983).
The dates given in this article refer to the Rotorua district in 1977 and 1978 and the timing of events in other parts of the country are likely to vary somewhat, being earlier in the north and later in the south or at higher altitudes.
Materials and Methods
Male and female sample trees of kahikatea, totara, Hall's totara, miro, matai and tanekaha were chosen with cone-bearing branches within reach from ground level or from a pruning ladder. All trees were within 30 km of Rotorua: miro trees were located in Dansey's Road, Hall's totara and matai on Fletcher's Road, tanekaha on Clinkard Road (all these being in the Mamaku area to the north-west of Rotorua); totara in the Forest Research Institute grounds, Whakarewarewa, Rotorua; and kahikatea at Te Ngae on the east of L. Rotorua.
Certain branches on the sample trees were tagged so that the ovules and cones they carried could be examined during each visit. Similar ovules and cones were collected from nearby branches for study.
Collecting visits were made on 18.11.77, 12.12.77, 21.3.78 and 14.8.78.
Results and Discussion
(Results are summarised in Table 1)
|Species||Reproductive cytcle||Dioecious or Monoecious||Dates ovules appear||Position of ovules||Date male cones appear||Position of male cones||Date of Pollination||Time until fertilisation||Fruit are ripe|
|Rimu||Long||D||Late spring (early Dec.)||Tips of existing shoots||Late spring (early Dec.)||Tips of existing shoots||January||± 12 months||March-May|
|Kahikatea||Short||D||October||Tips of existing shoots||October||Tips of existing shoots||mid October to November||2-3 months||March-May|
|Totara and Hall's totara||Short||D||October to November||Base of newly flushed shoot||End of previous season's growth (Break bud Oct-Nov)||On short lateral club-shaped shoot||November||2-3 months||March-May sometimes 2nd crop in spring|
|Miro||Long||Usually D||November||On short lateral shoots (usually single)||Late summer (visible all winter)||As lateral shoots (single)||November||± 12 months||March-May or later|
|Matai||Long||Usually D||November||In loose spikes with new spring||Late summer (visible all||In spikes||November to December||± 12 months||March-May|
|Tanekaha||Short||Usually M||October to November||On modified phylloclades||October to November||In whorls in place of phylloclades||November||2-3 months||March-May|
Table 1. Summary table of reproductive cycle of New Zealand tree podocarps. Rimu has been included in the table for completeness.
Kahikatea, Dacrycarpus dacrydioides
Kahikatea has a short reproductive cycle with the visible stages of cone and ovule development being completed in one growing season. The species is dioecious, the trees being either male or female, and in certain seasons, in spring time, October and November, the difference between the sexes may be seen from a distance. Male trees bear brown cones in such abundance that the whole tree may appear brownish, whereas female trees carry numerous glaucous ovules which give the tree a bluish tint. Sterile trees and branches appear bright green in spring when the new shoots are flushing.
Both male cones and ovules are produced terminally on the shoots. They develop rapidly in the spring and pollen is shed from mid October to November (Fig. 1).
The ovules are borne either singly or in pairs or occasionally threes in a specialised receptacle formed from the upper 2 or 3 leaves only (Figs. 2 and 3). The micropyle in kahikatea is directed towards the base of the ovule as in the young rimu ovule (McEwan. 1983), but in kahikatea the ovule-bearing shoot-tip is not upturned so the pollen falls from above almost directly towards the micropyle. The micropyle remains at the base of the mature seed, unlike rimu in which the micropyle is near the top of the mature seed.
During summer the ovule grows, fertilisation takes place (probably in January) and the seed expands and the surrounding epimatium (a modified ovuliferous scale) and carpidium (or bract-scale) ripen from March to May from a glaucous green to a dark purplish black, almost round seed, borne on a rounded red receptacle (Fig. 3 and 4).
In kahikatea neither the receptacle nor the male cone are stalked. Where a single seed is borne on each receptacle, one or two undeveloped ovules also occur, appearing as small glaucous protuberances (Fig. 4).
Totara, Podocarpus totara and Hall's Totara, Podocarpus hallii
These two species are closely related and have similar short reproductive cycles. Both are dioecious with separate male and female trees. Whereas in rimu and kahikatea there is no visible sign in winter of where male cones will appear the following spring, in the totaras distinctive small club-shaped shoots can be found on male trees on the previous season's growth. These consist of a minute male cone enclosed in several bud-scales and terminating a short stalk. The stalks of Hall's totara male cones are longer than those in true totara.
In spring the male cones break bud, expand rapidly and shed their pollen. In totara bud break occurs in late October and the male cone is somewhat elongated in shape. Pollen is shed in early November (Fig. 5).
In Hall's totara, which usually grows at higher altitudes than totara, bud break is in early December and pollination a few weeks later. The young male cone in Hall's totara is rounded in shape (Fig. 6).
Whereas the male cones develop as short specialised shoots at the end of summer and are visible in their buds throughout winter, the ovules in these species appear in the spring. They are situated towards the base of the new season's growth as it expands from the overwintering bud (Fig. 7). In both species the ovules are borne singly or in pairs on a specialised receptacle set on a short stalk. At the time of pollination the ovule plus receptacle and stalk is only about 3mm long in true totara (Fig. 8) and a little longer in P. hallii. The ovules are fully exposed and their micropyles are directed downwards towards the receptacle, as in kahikatea.
Development in both totara species is rapid, fertilisation occurring within several months of pollination and the fruit ripening between about March and May. The
Fig. 1 Male cones in kahikatea (mid October), shortly before pollination. Cones 5-8mm long. a. male cones.
Fig. 2. Ovules in kahikatea shortly before pollination (mid October). Ovules 1-2mm long. a. small glaucous ovules.
Fig. 3. Kahikatea ovule in mid October shortly before pollination. About 10 scale leaves surrounding the ovule have been removed. Whole structure 2mm long. The ovule is surrounded by the glaucous epimatium and half-covered by the carpidum which remains fused to it while the whole structure develops. a. bract, b. carpidium (green, slightly glaucous), c. epimatium surrounding ovule (glaucous), d. micropyle mouth (extension of integument).
Fig. 4. Ripe kahikatea fruit in late March, a. carpidum, b. dark purplish epimatium surrounding seed, c. red fleshy receptacle like a small raspberry. Receptacle and seed approx. 8mm.
Totara and Hall's Totara
Fig. 5. Male cones of true totara, two shedding pollen in early November. Note position of cones (indicated by arrow) in relation to the glaucous new spring growth.
Fig. 6. Male cones of Hall's totara breaking bud in December. On the right specimen a club-shaped shoot can be seen below the right hand cone. Male cones look like this during the preceding winter. Note the longer cone stalks and rounder shaped cones than in the true totara and the position of the cones in relation to the new spring growth.
Fig. 7. New ovules of true totara in mid October. Ovules occur on a receptacle set on a short stalk; they are found towards the base of the newly expanded new growth.
Fig. 8. New ovule (in mid October), set on a receptacle on a cone stalk and partially surrounded by a free, soft, scale-like carpidium. a. carpidium, b. micropyle just visible, c. ovule, d. receptacle, e. cone stak. Whole 5mm long.
Fig. 9. Ripe fruit of true totara (March). Note the rounded (green) seed and stalked receptacles, a. carpidium, b. green seed (4mm), c. red smooth succulent receptacle.
Fig. 10. Ripe fruit of Hall's totara (March). Note the elongated (green) seed. a. carpidium, b. green seed (5-6mm), c. orange-red smooth succulent receptacle.
In both species there may be a second flushing of shoots in late summer or autumn and a second crop of new ovules may be produced by female trees.
Club-shaped shoots may occasionally also burst into a second crop of male cones which pollinate the ovules. Such autumn pollinated ovules sometimes ripen in spring to produce seed with fleshy red receptacles (September-November).
It is also possible for unpollinated (and therefore unfertilised) ovules to develop ripe red receptacles either in autumn from a normal spring flushing, or in spring from an autumn flushing.
Miro, rumnopitys ferruginea (Podocarpus ferrugineus)
Miro, like rimu, has a long reproductive cycle (McEwen, 1983). The trees are usually dioecious but occasional trees are found which bear mostly ovules but have a few branches bearing male cones, and vice versa.
The ovule in miro develops on the previous season's growth on a special short shoot which appears like a tiny pinkish flower in November. The stalk has minute spiralled scales while the ovule itself is entirely surrounded by a glaucous epimatium and has several larger petal-like scales at its base. The whole structure is about 12mm long when pollinated in November (Fig. 11).
As in the totaras the male cones of miro are visible throughout winter (about 5mm long) (Fig. 12). They are carried on short stalks on the previous season's growth and appear like short waxy candles. These grow to about 15mm in the spring, before shedding pollen in November.
Fig. 11. Recently pollinated ovule of miro (December). Note the spiralled scales on the ovule stalk and the pinkish glaucous, petal-like scales (sterile carpidia) at the ovule base. a. ovule, b. scaled stalk (5mm).
Fig. 12. Immature male cones of miro (September). The cones are visible throughout winter and shed pollen in about November.
Fig. 13. Two stages of seed development in miro (March). The samll glaucous (green) ovule on the right is in its first season's growth, having been pollinated the previous November. The ripe (red) fruit on the left is a year older and fully developed.
After pollination the ovule begins to expand and its surrounding epimatium becomes a glaucous green. Most of the petal-like scales fall, leaving only one or two at the base of each ovule (Fig. 13). When it is about 5mm long the ovule ceases growth for a few months during winter, from about June to September. Fertilisation is thought to occur in December to January, more than 12 months after pollination.
Fig. 14. Two soft spikes of matai ovules, appearing like elongated cones (mid December).
Fig 15. Male matai cones close to pollen shed in late November.
Fig. 16. A spike of male cones of matai (April). These cones (1.5-2.5mm long) are visible throughout winter, a. cones (approx. 2mm long), b. subtending bract, c. leaf subtending male spike.
Fig. 17. Spike of matai ovules in their first year of development (April, following pollination in November). Several of the original ovules have aborted since the spike first appeared in November, a. carpidium, b. ovule (3mm), c. bract of aborted ovule.
Fig. 18. Two stages in seed development in matai (December). The two small ovules on the right were recently pollinated; the large (green) one on the left is in its second summer, pollinated over 12 months earlier and close to fertilisation. It will ripen to a dark purplish black seed in autumn. Note that most of the original 8 or so ouvles have aborted.
Matai, Prumnopitys taxifolia (Podocarpus spicatus)
Matai is closely related to miro and is similar in having a long reproductive cycle. Trees are usually either male or female but, as in miro, a few trees bear some reproductive organs of both sexes.
The male cones of matai are very conspicuous. Towards the end of summer small spikes develop, consisting of up to 18 cones arranged spirally on a lateral shoot. Each cone has a small bract-like leaf at its base and the whole spike is terminated by a cone. During winter the cones are between 1 and 2mm long (Fig 14).
The female structure is also spike-like and has up to 8 ovules, each borne in the axil of a small bract, arranged spirally on the axis. A pale green epimatium completely surrounds each ovule and the micropyle is directed downwards. These female structures, like elongated cones, appear in November as fragile new shoots (Fig. 15). Pollen is shed from the enlarged male cones in late November or early December (Fig. 16).
During summer some of the ovules grow but many of them abort or cease development during their first year (Fig. 17). They are about 3-5mm long when growth stops in June for several winter months. During the second summer ovules continue to expand and round out; fertilisation occurs probably in December or January (Fig. 18). In Fig. 18, taken in mid December, the two small ovules on the right are in their first season of growth and have recently been pollinated whereas the larger single ovule on the left is in its second growing season at approximately the time of fertilisation and should ripen by the following March.
Ripe matai fruits are about 8-10mm in diameter, rounded and dark purple or black. They are difficult to find, possibly because they are readily eaten by fruit eating birds such as New Zealand pigeons and tuis as soon as they are ripe.
Tanekaha, Phyllocladus trichomanoides
The reproductive cycle in tanekaha occupies only one year, as in kahikatea and the totaras. Tanekaha trees are usually monoecious, both male and female reproductive organs being borne on a single tree. However individual trees are often predominantly either male or female while also bearing a few cones of the opposite sex.
New phylloclades expand from the overwintering buds in spring (October or November) and some bear six or eight glaucous ovules with micropyles directed upwards (Fig. 19).
Groups of small purple male cones are produced at the same time in the place of groups of phylloclades (Fig. 20). Several weeks later pollen is shed from the expanded male cones and the ovules are pollinated by way of a pollination droplet (as is the case in the other podocarps). These droplets can be observed shining in the micropyles at the time of pollination. Fertilisation probably occurs in January and during the summer the ovule grows and develops into a shiny black seed. It is surrounded at the base by a cup-like structure, the aril (Fig. 21). When the seed ripens the aril becomes slightly swollen and white with a green frilly edge (Fig. 22).
Fig. 19. Specialised ovule-bearing phylloclades of tanekaha breaking bud in spring (October).
Fig. 20. Immature male cones of tanekaha having recently broken bud (October).
Fig. 21. Developing tanekaha seed (March).
Fig. 22. Close-up of two tanekaha fruits (March). The lower fruit is not quite mature and the white aril and dark seed has not fully emerged from the green receptacle whereas the upper fruit is fully ripe.
This attracts birds to eat and disperse the seed. A common feature of tanekaha however, is the large number of undeveloped or empty seeds and insect damage is common.
I thank members of staff of the Forest Research Institute, Rotorua: Messrs A.E. Beveridge and M.C. Smale for assistance and advice, H. Hemming and J. Barran for the photography and J. Leathwick for commenting on the text. I am grateful to Dr R. Sadlier, Director, Science and Research Directorate, Department of Conservation, for allowing me time to complete this work and to Dr B.V. Sneddon. Victoria University, for his constructive comments.
McEwen. W.M. 1983. Seed Production in Podocarp Trees. Forest and Bird 14: 23-24.