Reproductive and leaf morpho-anatomy of the Australian alpine podocarp and comparison with the Australis subclade

ABSTRACT

Podocarpus lawrencei (Mountain Plum Pine) is an endemic Australian conifer species and morphologically, ecologically, and genetically close to P. nivalis, P. gnidioides, P. totara, P. acutifolius, and P. laetus. The reproductive biology and seed cone morpho-anatomy of P. lawrencei and the Australis subclade is not well understood. This study describes the detailed reproductive morpho-anatomy of P. lawrencei and compares it with these related species of Australis subclade. Seed cone reproductive developmental stages, morpho-anatomical features of the seed cones and leaf were investigated using histology, light, and scanning electron microscopy.

Seed cone initiates with a terminal bud in late July, and the reproductive cycle takes 1 or more than 1 year (12–16 months) to complete. The ovule is inverted and ovule inversion is present. The reproductive cycle of this group of podocarps takes more than 1 year to complete. The seed cone of P. lawrencei has a fused non-fleshy epimatium (green-brown seed) with a brightly coloured reddish receptaculum. The seed cone shows morphological and anatomical similarity with P. nivalis in particular and no significant morpho-anatomical difference with other Australis subclade species. The brightly coloured fleshy cones of Australis subclade suggest frugivory and zoochory for dispersal of seeds. More extensive population genetic studies are required to evaluate the genetic structure, diversification, and historical biogeography of Australis subclade. This study provides a primary base from which to evaluate the genetic structure of all the species in this clade.

Graphical Abstract

KEYWORDS:

• Anatomy
• conifers
• endemic
• Podocarpaceae
• reproductive biology

Acknowledgments

We thank Adelaide Microscopy, the University of Adelaide for providing histology and microscopy facilities, and Mount Lofty Botanical Garden, SA, for seed cone collections.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

RK and RSH designed the study. RK conducted field and laboratory works and analysed data. RK and RSH drafted the manuscript.

Abbreviations

Rp = Receptaculum/Podocarpium, Ar = Aril, Em = Epimatium, Emr = Epimatium ridge, Fs = Fertile scale, Fsbr = Fleshy sterile bracts, Ax = Cone axis, Mi = Micropyle, Ov = Ovule, Ep = Epidermis, Gm = Gynophore membrane, Nu = Nucellus, Ts = Testa, Exo = Exotesta, Mes = Mesotesta, End = Endotesta, Mg = Megagametophyte, Emb = Embryo, Mi = Micropyle, Br = Bract, Sd = Seed, Vb = Vascular bundle, Rc = Resin canal, Rd = Resin duct, Pc = Pollen cone, Po = Pollen, Sc = Seed cone, Sl = Sclereid, Nc=Nucellar cap, In = integument, Cu = cuticle, St = Stomata, Gc = Guard cells, SE = scanning electron, SEM = scanning electron microscopy.