| Halocarpus C.J. Quinn 1982Common NamesTaxonomic notesType species: Halocarpus bidwillii (Hook. f. ex T. Kirk) C.J. Quinn (1)."This genus comprises three very closely related species, all endemic to New Zealand. As well as being distinguished by the inverted ovule, which has been used to link them with Podocarpus (Hooker 1843, Sahni and Mitra 1927), all species share the derived karyotype with only 16 major arms in the haploid component, compared with the haploid component of 20 arms that is basal in the family, occurring in all other species except Phyllocladus (Hair and Beuzenburg 1958). The distinction from Podocarpus is reinforced by the absence of fusion between the integument and the epimatium in Halocarpus, as well as in the presence of the aril-like collar. An aril also surrounds the base of the seed in the Phyllocladus, but the two structures do not appear homologous. The ovule is erect in the axil of the fertile bract in Phyllocladus and is devoid of an epimatium (Fig. 10). The aril arises at a late stage by an outgrowth from around the base of the ovule (Holloway 1937). It seems likely that this fleshy development evolved independently in the two groups as a mechanism to facilitate dispersal of the seeds by birds. "Other distinctive features of the genus are the flat, linear juvenile foliage, and the sterile cone apex first noted by Pilger (1903). The genus appears to be highly distinctive in the family, but shows some affinity with Lagarostrobos with which it shares the presence of 1 or 2 fenestroid cross-field pits in the secondary xylem, and an absence of hypodermis, vascular fibres and resin ducts in the leaves (Tengner 1965, Patel 1967). It shows no close affinity with Dacrydium s. str." (1). Description"Trees or shrubs with flat, linear juvenile leaves giving way abruptly to broad, imbricate, appressed scale leaves of the adult stage, though reversion foliage is common on adult plants. Male and female cones solitary, sessile and terminal. Female cones consisting of several elongated, leaf-like bracts, of which 1-5 are fertile, and terminating in a central sterile appendage (Fig. 11). Each fertile bract bears in its axil a prominent carpidium consisting of a single, inverted ovule with a membranaceous integument completely enclosed within its epimatium, the integument being free from the epimatium to the base of the ovule. The epimatium dorsiventrally compressed and striated, green at first, but becoming dark-brown to black at maturity while the region around the micropyle usually swells up to form a fleshy, white or slightly coloured, aril-like collar at the proximal end of the carpidium (Fig. 4). Seeds maturing in the second year" (1).The genus is "[s]imilar to Dacrydium ... only in having female cones borne on the ends of branches, but differs in the seed at maturity being inverted and completely invested by the epimatium without adnation, and the fertile scales never becoming swollen or fleshy, but rather the seed finally becoming surrounded at its micropylar end by a white collar produced from the epimatium" (1). RangeNew Zealand (1).Big TreeOldestDendrochronologyEthnobotanyObservationsRemarks"Halocarpus is named for the white collar at the base of the carpidium, which is the most striking feature of the genus" (1).See also Paleobotany of Australia and New Zealand conifers. Citations(1) Quinn 1982. | |
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