Caledonia) Monotypic Genus Species Is

Pacific capsular Myrtaceae 1. Reproductive morphology of Arillastrum gummiferumPanch. ex Baillon (New Caledonia) J.W. Dawson Botany Department, University of Wellington, New Zealand INTRODUCTION Niedenzu & Pfl. included the (in E. P., Nat. Fam. 3, 7, 1893, 87—89) following genera in his subtribe Metrosiderinae: Metrosideros, Spermolepis 2 (= Arillastrum), Lysicarpus, Cloëzia, Tepualia, Syncarpia, Xanthostemon, Pleurocalyptus, and Tristania. The Metroside- from the flowers rinae was distinguished Leptosperminae by usually having in axillary and from the broad based groups, not solitary, Eucalyptinae by having narrow, not petals. A preliminary survey of the above genera indicates that Niedenzu’s subtribe Metroside- rinae is in first examination not a natural group and this paper, the of a series, a critical of reproductive features of Arillastrum Panch. ex Baillon leads to the conclusion that this its is genus, notwithstanding narrow petal bases, most nearly related to the genera com- prising Niedenzu’s subtribe Eucalyptinae. Arillastrum a endemic to Caledonia. is a tree to is monotypic genus New It up 30 metres high and it was formerly common at lower elevations on serpentine terrainin the southern of the where often formed almost stands. The vernacular part island, it pure name for the species is ‘Chêne gomme’ (gum oak), which reflects both its value as timber and the abundance of a resinous secretion. The leaves (fig. 1) are opposite, with petioles several centimetres long and broadly dorsiventral laminae ovate, up to 13 X 10 cm. MORPHOLOGY Inflorescences The inflorescences of of on a branch develop in the axils the last 3—6 pairs leaves which terminates in a dormant vegetative bud. The subtending leaves become progressively reduced in size towards the branch tips (fig. 1). The are or 6 cm and broaden about —6 mm wide. peduncles up to 5 long distally to 5 They are strongly flattened dorsiventrally. The inflorescences are cymose and where the number in a group is large the lowermost have flowers with a reduction to for those the branch may 7 each, usually 3 nearer tip (fig. 2). The flowers are completely sessile. Each terminal flower is ebracteate and each Dr H. McKee and M. M. Veillon for the material which this *) I am very grateful to S. J. collecting on account is based. 2 ) SpermolepisBrongniart and Gris (Bull.Soc. Bot. Fr. io, 1863, 577) was invalid as Rafinesque (Neogenyt. 182$, 2) had already used the name for a genus of the Umbelliferae.Baillon (Hist. PI. 6, 1877, 363) adopted the name Arillastrum which was suggested the collector of the material. , originally by Pancher, type BLUMEA VOL. No. 432 XVIII, 2, 1970 — flower — Figs 2—10. Arillastrum gummiferum Panch. ex Baill. 2. Inflorescence with 3 buds, x 2½. 3. Habit of flower with circles: oil solid stamens removed, x 2½. — 4. Petal; open glands; spots: stone cells; — L. S. inner x 5. 5. flower through sepal to left and petal and and outerstamen groups to right; oil glands and oil tubes solid hr: — 6. Front outlined; spots: stone cells; hypanthial rim; is: inner stamens; x 4. view x — Rear view x anther, 32. 7. anther; og: oil gland; 32. — 8. Near median L. S. anther; og: oil gland; x 64. — 9. T. S. anther, x 64. — 10. Stigma, x 32. W. Dawson: J. Pacific Capsular Myrtaceae 1 433 lateral flower is subtended by a bract and has a pair of bracteoles at its base. The bracts and bracteoles are narrow, thick, and obliquely truncated at the tip (fig. 2). Perianth free and free imbricate the bud. The Each flower has 4 sepals 4 petals (fig. 3), in sepals thick and semi-orbicular with vascular strands at the base. The are usually 3 entering petals (fig. 4) are moderately thick, white to cream in colour, broadly rhomboidal to and almost orbicular narrowed to the base, where usually 3 vascular strands enter. Both sepals and petals have numerous scattered stone cells and spherical oil glands and in the adaxial sides. The addition continuous oil tubes accompanying veins on their sepals of which be and petals are inserted to the outside a continuous ledge may regarded as the tissue the surface of the upper rim of the largely nectar-secreting lining inner hypanthium. Stamens The stamens arise in 4 main, tangentially elongated groups from the hypanthial rim, of each the the centre group being situated inward from insertion of a petal (fig. 5, 18). almost meet front of the to 20 filaments Adjacent groups in sepals. They are up long at their outer edges and up to 10 filaments wide adjacent to the petal insertions. The of have anthers outermost 2 or 3 rows filaments no and are thus staminodes. They are twisted The coarse, long, and often irregularly (fig. 5). outermost stamens are usually only about half as long as the staminodes and the filaments of the other stamens become progressively shorter and more slender in an inward direction (fig. 5). There is no fusion staminodes. among the stamens or where the Between each main stamen group and the position hypanthial lining overlaps the there is smaller of fused in top of the ovary a group 10—20 stamens, irregularly 1 or 2 row(s) (fig. 5). Most of these inner stamens have an abnormal appearance with short filaments, narrowing abruptly from broad bases, and relatively large anthers of an irreg- form ular shape. Occasional appendages appear to be intermediate in between stamens and styles. The inner stamens curve outward while those of the outer groups curve inward. The dorsifixed and anthers of the normal stamens (fig. 6, 7) are versatile with 4 pollen of the sacs and longitudinal dehiscence. There is a single prominent oil gland at the tip the the the of the anther above insertion of filament (fig. 7, 8). At maturity epidermis anther has disappeared (fig. 8, 9). Style of the is The which is The free surface ovary nearly flat to moderately convex. style, the with not sunken into the apex of ovary, is short and solid a small convex stigma (fig. 5, 10). Placentation in is inferior There are 2 locules the ovary (fig. xi) which completely (fig. 5). The almost circular outline but to a at the placentas are axile, in narrowing point top. They bear in The small ovulodes ovules and ovulodes a distinctive pattern (fig. 12). occupy the and the of the and surround the less narrow upper part periphery placenta so more or centrally located ovules. There are about twice as many ovulodes as ovules, on an average the former the 24 of to 12 of latter. 434 BLUMEA VOL. XVIII, No. 2, 1970 Arillastrum Panch. Baill. — S. oil and oil tubes Figs 11—17. gummiferum ex 11. T. ovary; glands outlined; solid stone dotted circles: vascular x — of ovules and ovulodes spots: cells; bundles; 5. 12.Group ovulodes; stippled; x 12. — 13. L. S. ovule from open flower; light stipple: nuccllus and outer integument; dark inner stipple: integument; m: micropyle; es: embryo sac; the pigmented outer epidermis of the outer — from integumentis indicated by the broken line; x 70. 14. Ovule advanced flower bud; L. S. at right section angles to plane of of fig. 13; light stipple: nucellus and outerintegument; dark stipple: inner integ- — of ument; x 70. 15. Cell detail of integumentsand nucellus lined part in fig. 14; oi: outer integument; ii: inner — L. S. flower inner integument; n: nucellus; x 500. 16. ovulode from advanced bud; dark stipple: — L. S. integument; light stipple: outer integument; x 70. 17. ovulode from open flower; dark stipple: inner integument; light stipple: outer integument and nucellus; x 70. J. W. Dawson: Pacific Capsular Myrtaceae I 435 Fig. 1. Arillastrum gummiferum Panch. ex Baill. — Habit ofleaves and flowering and fruitingbranch tips. the ofthe x M.D. Vict. The arrow indicates dormant vegetative apex flowering branch; ½. (Photo King, Univ., Wellington). W. Dawson: J. Pacific Capsular Myrtaceae l 437 Ovules and ovulodes The ovules are campylotropous and crassinucellar with 2 integuments (fig. 13). On the of side the ovule furthest from the chalaza (fig. 14, 15) the outer integument is 6—8 cells thick and the cells thick. this the cells of the inner integument 2 At stage outer epidermis of the outer integument have brown contents, presumably tannin. Both integuments increase in thickness towards the chalaza. The ovulodes are also campylotropous with thick inner and outer integuments and a rudimentary nucellus (fig. 16, 17). Fruit The fruit The becomes very hard and woody (fig. 1). sepals are persistent and the scars of of the petals and outer, but not inner, groups stamens are usually discernable (fig. 18). The is into capsule splits open loculicidally and the style often split 2 parts, (fig. 18). Seeds Usually only one of the ovules in each locule matures into a fertile seed. It becomes it in more or less kidney-shaped and as takes up most of the space the locule, it becomes closely invested by the flattened, scale-like structures derived from the enlarged abortive ovules (fig. 18). The ovulodes mature into smaller structures which do not become so strongly flattened (fig. 20). 6 When the fertile seed is removed or 7 of the scales derived from the abortive ovules remain attached to it at the base by cobweb-like material (fig. 21). These scales were Pancher mistakenly interpreted by as an aril. The 'cobweb' is an open network of a transparent substance (fig. 22) with a pattern very similar to that of the epidermal cells of the scales. Perhaps it is derived from some substance secreted by the testa of the fertile seed which solidifies in the depressions external to the radial walls of the epidermal cells of the scales.

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