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Pittosporum halophilum Rock (Pittosporaceae: Apiales): Rediscovery, Taxonomic Assessment and Conservation Status of a Critically Endangered Endemic Species from Moloka`i, Hawaiian Islands. Pacific Science 65(4): 465–476.
Abstract
Pittosporum halophilum Rock originally was known only from the type
collections made in 1910 and 1911 along the windward sea cliffs of Moloka‘i. In
the most recent revision of Hawaiian Pittosporum it was treated as synonymous
with the more common species P. confertiflorum A. Gray. Since 1994, several
plants fitting the circumscription of P. halophilum have been discovered near the
type locality. Careful studies of these individuals and of plants cultivated from
their seeds clearly revealed that they are not only characterized by salt tolerance,
but differ from P. confertiflorum also in several other characters (i.e., a small,
shrubby habit; smaller leaves with cuneate bases and unique tan to golden yellow
wooly dense tomentum on abaxial leaf surfaces; shorter petioles; subcuboid to
ovoid capsules; and, in most individuals, functionally unisexual flowers). Based
on these substantial differences we conclude that P. halophilum merits recognition
on species level. In this paper we give a detailed description of P. halophilum
including remarks on its conservation status.
Pittosporaceae are a small family of flowering plants largely restricted to Australia, and entirely limited to the paleotropics. Two independent molecular datasets have been constructed with a representative sample from all nine genera of Pittosporaceae to test phylogenetic relationships suggested by recent morphological studies and to examine current morphological delimitations of genera. DNA sequence data derived from the ITS region of nuclear rDNA and from the trnL–trnF region of the chloroplast genome agree in uniting all species sampled from Pittosporum within a single clade, together with all species sampled from the previously segregated genus Citriobatus. Molecular data also confirm that members of the recently established genus Auranticarpa must be excluded from Pittosporum, and that another segregate genus, Sollya, should be placed within Billardiera. Hymenosporum remains a distinct, single-taxon lineage and Rhytidosporum is also confirmed as distinct. In most respects, our results are in agreement with recent taxonomic revisions based on morphology, and support an Australian origin of Pittosporaceae. Multiple dispersal events of Pittosporum from Australia to the islands of the Pacific and Indian Oceans, including New Zealand, are suggested, as well as island hopping throughout the Pacific.
Following a phylogenetic analysis using morphology,
Pittosporum is here monographed and recircumscribed as a
monophyletic genus, by including the small genus
Citriobatus and by excluding a new genus, described in
the accompanying paper as Auranticarpa. Within Australia
and its associated territories, 20 species are now recognised in
Pittosporum, including the four from
Citriobatus, three of which are given new combinations
(P. spinescens, P. lancifolium and
P. multiflorum).
Citriobatus linearis requires a new name
(P. viscidum). Four species are reinstated or confirmed
at species level (P. angustifolium,
P. ligustrifolium, P. nativitatis
and P. wingii), and P. trilobum is
described for the first time.
Microsatellites (SSR--simple sequence repeats, STR--short tandem repeats, SSLP--simple sequence length polymorphism, VNTR--variable number of tandem repeats) are the class of repetitive DNA sequences present in all living organisms. Particular characteristics of microsatellites, such as their presence in the genomes of all living organisms, high level of allelic variation, co-dominant mode of inheritance and potential for automated analysis make them an excellent tool for a number of approaches like genotyping, mapping and positional cloning of genes. The three most popular types of markers containing microsatellite sequences that are presently used are: (1) SSR (simple sequence repeats), generated by amplifying in a PCR reaction with the use of primers complementary to flanking regions; (2) ISSR (inter-simple sequence repeats), based on the amplification of regions between inversely oriented closely spaced microsatellites; and (3) SAMPL (selective amplification of microsatellite polymorphic loci), which utilises AFLP (amplified fragment-length polymorphism) methodology, with one exception--for the second amplification, one of the starters is complementary to the microsatellite sequence. The usefulness of the three above-mentioned markers for numerous purposes has been well documented for plants.
In this paper chromosome counts for 90 collections representing 67 native Hawaiian angiosperm species and eight hybrids in 22 families are presented and discussed. Included are the first records for 26 species, two sub- specific taxa, eight natural hybrids, and the endemic genus Pteralyxia (Apocyna- ceae). In four families Hawaiian representatives have been investigated cytologically for the first time. For three species the investigations are the first on Hawaiian material. Seven counts differ from earlier reports in the literature. Implications of the results are discussed in the context of autochthonous chro- mosomal evolution and of colonization events for the Hawaiian Islands. Chromosome numbers are available for nearly 40% of the native Hawaiian species (Carr 1998). In most cases these numbers were obtained from counts of single or very few individuals. In this paper it is aimed to improve the knowledge on chromosome numbers for Hawaiian angiosperms, both with regard to taxa not previously investi- gated and for additional collections of taxa already counted. Data for 19 species pre- sented here were shared with G. Carr (Uni- versity of Hawai'i at Manoa, Honolulu) and were included in his earlier survey (Carr 1998, table 1.1) as ''Kiehn unpubl.'' These counts are documented and discussed further here and are footnoted ''c'' in Table 1.
Any conservation actions that preserve some populations and not others will have genetic consequences. We used empirical data from four rare plant taxa to assess these consequences in terms of how well allele numbers ( all alleles and alleles occurring at a frequency openface>0.05 in any population ) and expected heterozygosity are represented when different numbers of populations are conserved. We determined sampling distributions for these three measures of genetic diversity using Monte Carlo methods. We assessed the proportion of alleles included in the number of populations considered adequate for conservation, needed to capture all alleles, and needed to meet an accepted standard of genetic-diversity conservation of having a 90–95% probability of including all common alleles. We also assessed the number of populations necessary to obtain values of heterozygosity within ±10% of the value obtained from all populations. Numbers of alleles were strongly affected by the number of populations sampled. Heterozygosity was only slightly less sensitive to numbers of populations than were alleles. On average, currently advocated conservation intensities represented 67–83% of all alleles and 85–93% of common alleles. The smallest number of populations to include all alleles ranged from 6 to 17 ( 42–57% ), but <0.2% of 1000 samples of these numbers of populations included them all. It was necessary to conserve 16–29 ( 53–93% ) of the sampled populations to meet the standard for common alleles. Between 20% and 64% of populations were needed to reliably represent species-level heterozygosity. Thus, higher percentages of populations are needed than are currently considered adequate to conserve genetic diversity if populations are selected without genetic data.
We investigated the origin of Hawaiian Pittosporum and their relationship to other South Pacific Pittosporum species using internal transcribed spacer sequences of nuclear ribosomal DNA. We performed both maximum-parsimony and maximum-likelihood analyses, which produced congruent results. Sequence divergence was 0.0% between Hawaiian members of Pittosporum. These taxa formed a strongly supported clade, suggesting a single colonization event followed by phyletic radiation. Sister to the Hawaiian clade were two South Pacific species, P. yunckeri from Tonga and P. rhytidocarpum from Fiji. This result presents convincing evidence for a South Pacific origin of Hawaiian Pittosporum. Our results also identify a monophyletic group comprising three species representing the Fijian Province and East Polynesia, two introductions onto New Caledonia, and at least one (but possibly two) introduction(s) onto New Zealand. Whether the New Zealand taxa form a monophyletic group is unclear from these data. Previous morphologically based hypotheses, however, suggest the presence of four different lineages occupying New Zealand. The nonmonophyly of the New Caledonian species was not surprising based on the extent of their morphological diversity. Although this latter result is not strongly supported, these species are morphologically complex and are currently the subject of taxonomic revision and molecular systematic analyses.
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