Abstract:
Arthrocardia is a genus of articulated coralline algae (Corallinophycidae, Rhodophyta), a group
of calcified red macroalgae that provides critical ecosystem services but is vulnerable to various
anthropogenic disturbances. Studying its ecological roles and responses to environmental changes
requires accurate taxonomic information, but unfortunately, the taxonomic status of Arthrocardia
in New Zealand remains ambiguous. Until recently, two Arthrocardia species (A. corymbosa and
A. wardii) were reported in New Zealand based on morphological identification. However, recent
molecular analyses established the presence of three Arthrocardia species (temporarily named
Arthrocardia spp. A, B, and C), although their morphoanatomy and distribution had not been
characterised yet. This study employed an integrative taxonomic approach to characterise and
compare New Zealand Arthrocardia and determine whether morphoanatomical differences and
geographic distributions correspond to the species boundaries established molecularly.
Multivariate analyses revealed that morphoanatomy is not taxonomically informative, although
ANOVA showed that a few characters may help distinguish Arthrocardia sp. B from Arthrocardia
sp. C, and Arthrocardia from its sister genus Corallina. Likewise, using geographic distribution
alone is not reliable in distinguishing the three species. These results indicate that
morphoanatomical differences and geographic distribution are not always congruent with
molecular findings and thus have limited taxonomic use. Thus, molecular analyses are necessary
for reliable identification and segregation of New Zealand Arthrocardia species. The
morphoanatomical and geographic distribution data collected in this study are valuable in
investigating whether the species names A. corymbosa and A. wardii, based on South African and
Australian types, apply to New Zealand specimens. Lastly, this research provides baseline data
for ecological and environmental studies that involve Arthrocardia in New Zealand.