New Zealand Journal of Botany

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Hermaphroditism and dichogamy in polaris () on Campbell Island

JM Lord

To cite this article: JM Lord (2012) Hermaphroditism and dichogamy in Stilbocarpa polaris (Araliaceae) on Campbell Island, New Zealand Journal of Botany, 50:1, 89-93, DOI: 10.1080/0028825X.2011.638645 To link to this article: https://doi.org/10.1080/0028825X.2011.638645

Published online: 06 Mar 2012.

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Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tnzb20 New Zealand Journal of Botany Vol. 50, No. 1, March 2012, 89Á93

Hermaphroditism and dichogamy in Stilbocarpa polaris (Araliaceae) on Campbell Island JM Lord* Department of Botany, University of Otago, Dunedin, New Zealand (Received 27 September 2011; final version received 1 November 2011)

Since its scientific discovery in 1844, the breeding system of Stilbocarpa polaris (Araliaceae) has been described as polygamo-dioecious with either unisexual or hermaphroditic and female flowers. A short study of flower sex expression, on subantarctic Campbell Island, found evidence that all flowers are cosexual, protandrous and strictly dichogamous, such that whole inflorescences are either presenting pollen or stigmas. Circumstantial evidence also suggests that S. polaris is self-compatible but self-fertilisation would be largely avoided by this synchronous dichogamy. Pollination is most likely effected by small diptera which congregate on inflorescences. Keywords: breeding system; dioecy; hermaphroditism; megaherb; subantarctic

Introduction segregate genus, Kirkophytum, in Allan (1961) Stilbocarpa is a genus of megaherbs restricted for which the breeding system was described as to the extreme southern tip of the New Zealand monoecious or polygamo-dioecious. mainland and the subantarctic islands. Descriptions of the breeding system of can reach more than 1 m in height, with leaves S. polaris and depictions of the gender of up to 40 cm wide. Inflorescences are borne individual flowers vary in the historic botanical on robust stalks and can consist of hundreds literature. Stilbocarpa polaris was originally of florets arranged in a compound umbel named Aralia polaris by JB Hombron and (Fig. 1A). In various Floras of New Zealand M Jacquinot (Hombron et al. 1852) when the (e.g. Kirk 1899; Cheeseman 1906; Allan 1961) was encountered during the southern the breeding system of Stilbocarpa polaris voyages of the Astrolabe. The illustration of has been described as polygamous, polygamo- A. polaris in Hombron et al. (1852) shows what dioecious and polygamo-monoecious. These appears to be a hermaphrodite flower and a terms indicate that hermaphrodite, staminate female flower, but no legend is provided along- and pistillate flowers can occur on the same side the plate. The first full species description (polygamo-monoecious), or that herma- was that of JD Hooker in Flora Antarctica phrodite and either staminate or pistilate (1844) in which he describes the breeding flowers can occur on the same plant (polygamo- system as polygamous. A detailed illustration dioecious) or on the same as well as separate of flowers and fruit of A. polaris appears in Sir plants (polygamous) (Sakai & Weller 1999). William Hooker’s Icones Plantarum (1848) and The two other currently described Stilbocarpa the legend to the plate identifies the illustrations species, S. lyallii and S. robusta, were listed as a as showing a ‘young perfect flower’ and a

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ISSN 0028-825X print/ISSN 1175-8643 online # 2012 The Royal Society of New Zealand http://dx.doi.org/10.1080/0028825X.2011.638645 http://www.tandfonline.com 90 JM Lord

Figure 1 Stilbocarpa polaris, Campbell Island. A, near Beeman Base. B, Floret presenting pollen. Immature styles can be seen tightly packed in the centre of each floret. C, Umbel presenting stigmas. Stamens have detached and styles have unfurled. Photograph in B courtesy Peter Heenan.

‘female flower’, which W. Hooker states were polygamous. Kirk (1884) in an article concern- ‘drawn on the spot from the recent plant’. The ing punui (S. lyallii) provides illustrations of species appears as S. polaris in JD Hooker’s S. polaris flowers but describes them as stami- Handbook of the New Zealand Flora (1864) and nate and pistillate ‘after Hooker’. Further, the genus as a whole is described there as he refers to male and female flowers in the Hermaphroditism and dichogamy in Stilbocarpa polaris (Araliaceae) on Campbell Island 91 description of S. polaris in his Students’ Flora of stigmatic surfaces (Fig. 1C). Flowers were New Zealand and the Outlying Islands (1899) clearly protandrous, with all flowers in and describes the genus as having ‘huge masses an inflorescence coordinated (synchronous of unisexual or polygamous flowers’. This shift protandry). In young inflorescences, central to representing S. polaris flowers as unisexual clusters in each umbel consisted of flowers continues in Cheeseman’s Illustrations of the presenting pollen while flowers in peripheral New Zealand Flora (1914) in which the legend clusters were still in bud. These central flowers to the plate lists a male flower and a female remained in the pollen-presentation phase as flower. In Cheeseman’s Manual of the New younger flowers opened. Because of the limited Zealand Flora (1906) the genus Stilbocarpa is length of the study, inflorescences on only one described as being polygamo-monoecious. plant were directly observed to change from In this short note, I report the results of pollen to stigma presentation, so it appears that observations made of the structure and sex the pollen-presentation phase of an inflores- expression of florets on a number of S. polaris cence as a whole could last for at least 10 days. individuals on Campbell Island that throw new Transition from pollen to stigma presentation light on these descriptions of its breeding only occurred after anther senescence; no plant system. was found with central flowers presenting stigmas and peripheral flowers still releasing pollen, nor was any plant found with both Methods stigma-presenting flowers and buds present. Clusters of flowers from the central and peri- Flowers with newly unfurled stigmas possessed pheral parts of umbels were collected from the remains of previously dehisced anthers, eight individual plants of S. polaris occurring however, these detached readily so that most around Beeman Base and the Col-Lyall Saddle, flowers presenting stigmas showed no obvious south-east Campbell Island, over a 10-day evidence of anthers having been present and the period in late November to early December scars at the site of filament attachment were 2010. Each flower was dissected under a only visible under high magnification. microscope and the presence and developmen- Old infructescences were found beneath all tal stage of the sex organs were recorded. plants bearing new inflorescences. Fruit and Representative photographs were taken of fruit remnants still adhering to the infructes- flowers at different stages. Three plants close cence stalks were consistently well formed with to Beeman Base were visited repeatedly during visible seeds or clear evidence of seeds having the study period and flower development and been present. sex expression noted. All plants were also inspected for remnants of infructescences from the previous flowering season. Discussion This study confirms that S. polaris flowers are generally cosexual and protandrous. His- Results toric interpretations of the breeding system as All buds and young flowers examined possessed involving varying types of unisexual flowers a ring of five deciduous stamens around the undoubtedly arose due to the strict dichogamy outer edge of the receptacle and an inner ring of and length of pollen and stigma presentation, three to six styles. In young flowers, styles were combined with the limited time most botanists so tightly compressed in the centre of the flower had to observe and collect material. It is not that they were often difficult to see (Fig. 1B). difficult to see how the sex expression of Following anther dehiscence, the stamens S. polaris might have been mistaken for poly- detached and the styles unfurled to expose the gamodioecy, especially as much of the material 92 JM Lord examined would have been pressed and dried, Acknowledgements and due to the highly synchronous nature We thank the Department of Conservation for of flower development, only one phase of sex permission to work on Campbell Island; Henk expression is likely to have been visible on each Haazen, captain of Tiama and the captain and umbel. The observations made during this study crew of HMNZS Otago for transport; Lynne do not support gynodioecy, as old anthers were Huggins, Lorna Little and Vickey Tomlinson for observed still attached to flowers newly present- assistance in the field; Colin Webb for helpful ing stigmas and no buds were observed on comments on an earlier draft. plants bearing only stigma-presenting flowers. This study is not the first to disagree with References the description of the breeding system of Allan HH 1961. Flora of New Zealand, Volume 1. S. polaris given in Allan (1961) and other floras. Wellington, Government Printer. p. 1085. Stilbocarpa is not mentioned in Godley’s dis- Allen AM, Hiscock SJ 2008. Evolution and cussion of gender dimorphism in the New phylogeny of self-incompatibility systems in Zealand flora (1979), however, Godley reported angiosperms. In: Franklin-Tong VE ed. 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