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Flower Structure
The flower of Thymelaeaceous plants is considered by Heinig (1951) to be an expanded torus, with the calyx at the end of the floral tube. The flower is best referred to as the flower tube, and this term will be used in future discussion of Pimelea flowers.
A description of the flowers of one of the Pimelea species at Cass, in general terms, will cover all of them, except in gross dimensions, since little other difference is to be seen in flowers from different species.
Flowers are terminal and grow erect in dense heads of 10–20 flowers. They are almost sessile on very short stalks, and at the base of the flowers is a dense growth of silky hair which remains after the fruit has fallen. The flower tube is cylindrical, with four calyx lobes at the distal end of a hollow tubular torus. The lobes are small and spreading when the flowers are open. Petals are absent, but the torus is petaloid. The upper side of the calyx lobes and inside of the floral tube is waxy white and usually glabrous (some hairs may be found, especially in P. traversii, inside the tube) and bears very small tubercles which give a shining appearance. The outer wall of the flower tube and underside of the calyx lobes are densely clothed with simple hairs. The base of the tube, surrounding the ovary, is red in P. prostrata, P. “snow tussock” and P. “short tussock” Especially in female flowers this area is often folded, and bulging. The hermaphrodite flower tube base bulges less and is narrower and longer than in females. The hermaphrodite flower tube base bulges less and is narrower and longer than in females. The flowers of P. prostrata, P. “short tussock” and P. “snow tussock” have a distinctly sweet scent, but the scent of P. traversii is negligible Nectar is produced in both females and hermaphrodites, apparently by morphologically unspecialised cells on the inner walls of the flower tube. It lies here, about half way up the tube or at the bottom of the tube.
Measurements of the long axis of flower tubes in from 20–30 plants (average of 5 flowers per plant) in both sexes of each species at Cass are given below.
In all cases the hermaphrodite flower tubes are larger than the female ones, although in any one species, a few individuals of either sex approach one another in size. Other structural differences between hermaphrodite and female are also
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| Species | Mean Flower Tube Length | Range | Standard Deviation |
|---|---|---|---|
| P. “snow tussock” ☿ | 5.4mm | 4.5–6.5mm | 0.65 |
| P. “snow tussock” ♀ | 3.3mm | 2.2–4.1mm | 0.45 |
| P. “short tussock” ☿ | 4.4mm | 3.5–5.2mm | 0.49 |
| P. “short tussock” ♀ | 3.0mm | 2.4–3.8mm | 0.36 |
| P. prostrata ☿ | 4.0mm | 2.6–4.9mm | 0.43 |
| P. prostrata ♀ | 2.6mm | 2.1–3.0mm | 0.28 |
| P. traversii ☿ | 7.4mm | 6.2–8.5mm | 0.93 |
| P. traversii ♀ | 4.8mm | 4.0–6.0mm | 0.53 |
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obvious. Stamens are two in number in hermaphrodit flowers and inserted just below the throat of the floral tube, opposit the two outer lobes. Filaments are slender and the anthers extend straight above the flower tube for 2–3 mm and face inward. Dehiscence of anthers in the hermaphrodite allows pollen to fall into the flower tube. In the female stamens are withered and filaments are shorter. Shrivelled pollen is found in a few cases.
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The ovary in both female and hermaphrodite is one-celled and the slender style rises from one side of it, near its summit. During the period after opening of the flower, the style, which lies to one side of the floral tube, begins to elongate. Eventu|ally, if the flower is unpollinated, it may extend from 1/2 - 3/4 of the length of the floral tube beyond the mouth of the tube. The stigma of the female flower is more than twice as wide as that of the hermaphrodite, and its simple papillae are also longer. They are twice the lengeth of those of the hermaphrodite and extend radially from the centre. (See Fig. 1.) In a few cases hermaphrodite plants carried a few female flowers in the heads of hermaphrodite flowers. Some such mixed heads had a few flowers of intermediate dimensions and with characters of both sexes.
The upper part of the ovary is hairy. After fertilization the ovary begins to swell and in P. “snow tussock”, P. “short tussock” and P. prostrata the growth is sufficient to burst the persistent base of the flower tube. This serves as a loose outer coat, becoming glabrous brown and straite, but soon falls away. Although the tube does not appear to be articulate between base and upper tube, it often breaks here.
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| Species | Number of ☿ plants | Number of ♀ plants | Ratio ☿ ♀ | |
|---|---|---|---|---|
| Cass | ||||
| P. “snow tussock” early in season | 47 | 49 | 1 : 1 | |
| P. “-snow tussock” late in season | 41 | 38 | 1 : 1 | |
| P. “short tussock” early in season | 41 | 39 | 1 : 1 | |
| P. “short tussock” late in season | 35 | 35 | 1 : 1 | |
| P. prostrata early in season | 54 | 35 | 1.54 : 1 | |
| P. prostrata late in season | 42 | 22 | 2 : 1 | |
| P. traversii early in season | 32 | 25 | 1.28 : 1 | |
| P. traversii late in season | 43 | 23 | 2 : 1 | |
| Erewhon | ||||
| P. “snow tussock” early in season | 44 | 22 | 2 : 1 | |
| P. prostrata early in season | 60 | 10 | 10 : 1 | |
| Macaulay River | ||||
| P. “snow tussock” | 47 | 24 | 2 : 1 | |
| P. prostrata | 55 | 18 | 3 : 1 | |
| Lake Tekapo | ||||
| P. “snow tussock” | 37 | 33 | 1 : 1 |
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In P. “snow tussock”, P. “short tussock” and P. prostrata only the base is left, but in P. traversii the whole hairy flower tube is left surrounding the ovary, although not adherent to it.
The fruits of P. “snow tussock” and P. “short tussock” are oval, yellow, orange, or red and fleshy. They are somewhat flattened laterally, and the seed, black, hard and oval, is imbedded in the fleshy portion. Fruits of P. prostrata are similar in size, but snow white and fleshy. In these plants fruits are produced in large numbers in crowded clusters. Very few of the flowers of females do not produce fruit. In P. traversii there is a small green, hard fruit. Fruits are quickly shed when ripe from all four species.