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Floral scent often intensifies during periods of pollinator activity, but the degree of this synchrony may vary among scent compounds depending on their function. Related plant species with the same pollinator may exhibit similar timing and composition of floral scent. We compared timing and composition of floral volatiles for two endemic Hawaiian plant species, Schiedea kaalae and S. hookeri (Caryophyllaceae). For S. kaalae , we also compared the daily timing of emission of floral volatiles to evening visits of their shared pollinator, an endemic Hawaiian moth ( Pseudoschrankia brevipalpis ; Erebidae). The identity and amount of floral volatiles were measured in the greenhouse during day and evening periods with dynamic headspace sampling and GC-MS (gas chromatography – mass spectrometry). The timing of emissions (daily rise, peak, and fall) was measured by sampling continuously for multiple days in a growth chamber with PTR-MS (proton transfer reaction mass spectrometry). Nearly all volatiles detected underwent strong daily cycles in emission. Timings of floral volatile emissions were similar for S. kaalae and S. hookeri , as expected for two species sharing the same pollinator. For S. kaalae , many volatiles known to attract moths, including several linalool oxides and 2-phenylacetaldehyde, peaked within 2 h of the peak visitation time of the moth which pollinates both species. Floral volatiles of both species that peaked in the evening were also emitted several hours before and after the brief window of pollinator activity. Few volatiles followed a daytime emission pattern, consistent with increased apparency to visitors only at night. The scent blends of the two species differed in their major components and were most distinct from each other in the evening. The qualitative difference in evening scent composition between the two Schiedea species may reflect their distinct evolutionary history and may indicate that the moth species uses several different floral cues to locate rewards.

During a survey by the National Tropical Botanical Garden drone team, an enigmatic Schiedea was observed in December 2021on steep, rocky cliff faces of the Waiahulu Valley in the Waimea Canyon of Kaua'i. Subsequently, another survey was conducted in March 2022 and, by use of a remotely controlled cutting device suspended below the drone, the first herbarium specimen was collected, as well as a seed collection of an undescribed cliff-dwelling species of Schiedea . Detailed study of the collections and plants grown at the University of California, Irvine greenhouse showed that it had enlarged, somewhat whitish sepals similar to those of cliff-dwelling S. attenuata (the sole species in sect. Leucocalyx), yet differed significantly from all other species in the genus. It also shares with S. attenuata a woody habit, hermaphroditic flowers, coloured nectar and styles 5 to 7 or 8. We describe it here as S. waiahuluensis given the only known localities are on the cliffs of this valley and place it in an enlarged sect. Leucocalyx. With the discovery of this new species, there are 36 species in this Hawaiian endemic genus.

Many insular plant taxa naturally consist of small populations, which are increasingly impacted today by herbivory, climate change, and competition with invasive plants. Are some insular species fated to extinction or do they still have potential to recover? To help explore this question, we studied Schiedea adamantis, a federally endangered shrub from the Hawaiian island of O‘ahu where it was originally known as a single population. This population underwent a population crash in the late 1990s, declining from >250 plants to a handful of plants before several more individuals were discovered nearby. Fortunately, plants grown from seed obtained before the bottleneck had been maintained ex situ in California. Using microsatellite markers, we confirmed that levels of genetic variation were lower in the bottlenecked population compared to the pre-bottleneck and offspring collections, but overall levels remained moderate in the wild population despite the severe reduction in size. The four remaining field individuals consisted of one plant that likely persisted through the bottleneck and its progeny. The ex situ offspring collection contained four unique alleles, indicating the value of these collections maintained offsite. Subsequently, new plants located downslope from the original population and a second genetically different population on the same island were also discovered, although numbers continue to decline. In addition to ongoing reintroduction efforts, levels of genetic variation and discovery of new individuals holds promise for in situ survival of this species, but only if its habitat can be protected from fire, increased drought, and competition from invasive species.

Many insular plant taxa naturally consist of small populations, which are increasingly impacted today by herbivory, climate change, and competition with invasive plants. Are some insular species fated to extinction or do they still have potential to recover? To help explore this question, we studied Schiedea adamantis, a federally endangered shrub from the Hawaiian island of O'ahu where it was originally known as a single population. This population underwent a population crash in the late 1990s, declining from >250 plants to a handful of plants before several more individuals were discovered nearby. Fortunately, plants grown from seed obtained before the bottleneck had been maintained ex situ in California. Using microsatellite markers, we confirmed that levels of genetic variation were lower in the bottlenecked population compared to the pre-bottleneck and offspring collections, but overall levels remained moderate in the wild population despite the severe reduction in size. The four remaining field individuals consisted of one plant that likely persisted through the bottleneck and its progeny. The ex situ offspring collection contained four unique alleles, indicating the value of these collections maintained offsite. Subsequently, new plants located downslope from the original population and a second genetically different population on the same island were also discovered, although numbers continue to decline. In addition to ongoing reintroduction efforts, levels of genetic variation and discovery of new individuals holds promise for in situ survival of this species, but only if its habitat can be protected from fire, increased drought, and competition from invasive species.

In 2016 during a survey for potential fencing of the Ha‘akoa unit on windward Mauna Kea, Hawai‘i Island (Hawaiian Islands) a single plant of the genus Schiedea was discovered. No species of the genus had ever been known to occur in this area, and only three species of Schiedea were known previously from Hawai‘i Island. Two are vining species and the third is a coastal subshrub. The single plant obviously represented an interesting find, and because the plant was vegetative another visit was scheduled to collect a flowering specimen, but by then the plant had died. Soil taken from the site with seeds in the soil produced two plants, one of which flowered in cultivation in 2021. A study of this individual indicated it was a member of Schiedea sect. Mononeura, characterized by erect to ascending habit, quadrangular stems, seeds not persistent on the placenta and readily dispersing from the dehisced capsule, and flowers facultatively autogamous. With the discovery of this new species there are 35 species in this Hawaiian endemic genus.

Shifts in pollination may drive adaptive diversification of reproductive systems within plant lineages. The monophyletic genus Schiedea is a Hawaiian lineage of 32 extant species, with spectacular diversity in reproductive systems. Biotic pollination is the presumed ancestral condition, but this key element of the life history and its role in shaping reproductive systems has remained undocumented. We observed floral visitors to two species of Schiedea and conducted field experiments to test pollinator effectiveness. We used choice tests to compare attraction of pollinators to species hypothesized to be biotically vs wind-pollinated. Pseudoschrankia brevipalpis (Erebidae), a recently described moth species known only from O‘ahu, visited hermaphroditic Schiedea kaalae and S. hookeri and removed nectar from their unique tubular nectary extensions. Pseudoschrankia brevipalpis effectively pollinates S. kaalae; single visits to emasculated flowers resulted in pollen transfer. In choice tests, P. brevipalpis strongly preferred these hermaphroditic species over two subdioecious species capable of wind pollination. A shift from biotic to abiotic pollination is clearly implicated in the diversification of reproductive systems within Schiedea. Abundant pollination by a previously unknown native moth in experimental and restored populations suggests the potential for restoration to re-establish native plant–pollinator interactions critical for production of outcrossed individuals with high fitness.

During a survey by the National Tropical Botanical Garden drone team, an enigmatic was observed in December 2021on steep, rocky cliff faces of the Waiahulu Valley in the Waimea Canyon of Kaua'i. Subsequently, another survey was conducted in March 2022 and, by use of a remotely controlled cutting device suspended below the drone, the first herbarium specimen was collected, as well as a seed collection of an undescribed cliff-dwelling species of . Detailed study of the collections and plants grown at the University of California, Irvine greenhouse showed that it had enlarged, somewhat whitish sepals similar to those of cliff-dwelling (the sole species in sect. Leucocalyx), yet differed significantly from all other species in the genus. It also shares with a woody habit, hermaphroditic flowers, coloured nectar and styles 5 to 7 or 8. We describe it here as given the only known localities are on the cliffs of this valley and place it in an enlarged sect. Leucocalyx. With the discovery of this new species, there are 36 species in this Hawaiian endemic genus.

Asymmetrical gene flow, which has frequently been documented in naturally occurring hybrid zones, can result from various genetic and demographic factors. Understanding these factors is important for determining the ecological conditions that permitted hybridization and the evolutionary potential inherent in hybrids. Here, we characterized morphological, nuclear, and chloroplast variation in a putative hybrid zone between Schiedea menziesii and S. salicaria, endemic Hawaiian species with contrasting breeding systems. Schiedea menziesii is hermaphroditic with moderate selfing; S. salicaria is gynodioecious and wind-pollinated, with partially selfing hermaphrodites and largely outcrossed females. We tested three hypotheses: 1) putative hybrids were derived from natural crosses between S. menziesii and S. salicaria, 2) gene flow via pollen is unidirectional from S. salicaria to S. menziesii and 3) in the hybrid zone, traits associated with wind pollination would be favored as a result of pollen-swamping by S. salicaria. Schiedea menziesii and S. salicaria have distinct morphologies and chloroplast genomes but are less differentiated at the nuclear loci. Hybrids are most similar to S. menziesii at chloroplast loci, exhibit nuclear allele frequencies in common with both parental species, and resemble S. salicaria in pollen production and pollen size, traits important to wind pollination. Additionally, unlike S. menziesii, the hybrid zone contains many females, suggesting that the nuclear gene responsible for male sterility in S. salicaria has been transferred to hybrid plants. Continued selection of nuclear genes in the hybrid zone may result in a population that resembles S. salicaria, but retains chloroplast lineage(s) of S. menziesii.

• Premise of the study: Reintroductions may be essential to prevent extinction of many critically endangered species. Ideally, reintroduction efforts rely on adjacent source populations, but limited source material may necessitate crossing individuals from different and possibly distant populations. To determine the consequences of integrating multiple populations in reintroductions, we investigated levels of inbreeding depression, outbreeding depression, and heterosis for populations of Schiedea kaalae (Caryophyllaceae), an endangered species endemic to the Wai‘anae and Ko‘olau Mountains of O‘ahu, Hawai‘i. The possibility of gene flow among plants was explored through pollinator observations.• Methods: Individuals from ex situ living collections of nine populations were hand-pollinated with pollen from the same plant, plants from the same population (for three populations only), or plants from different populations. Progeny were outplanted into two common gardens, one in each mountain range on O‘ahu. Cumulative fitness was estimated using several independent life history stages.• Key results: Inbreeding depression was minimal, and no outbreeding depression was detected. In contrast, strong heterosis was evident in progeny from between-population crosses, which had higher relative fitness than progeny from self-pollinations or within-population crosses. Observations of floral visitors provided the first evidence that biotic pollination may be important for this species.• Conclusions: Results demonstrate the ability to conduct genetic rescue of rare species and suggest that reintroductions may be most successful using heterotic individuals from crosses between populations and at sites where pollinators are present and promote outcrossing.

In 2016 during a survey for potential fencing of the Ha'akoa unit on windward Mauna Kea, Hawai'i Island (Hawaiian Islands) a single plant of the genus was discovered. No species of the genus had ever been known to occur in this area, and only three species of were known previously from Hawai'i Island. Two are vining species and the third is a coastal subshrub. The single plant obviously represented an interesting find, and because the plant was vegetative another visit was scheduled to collect a flowering specimen, but by then the plant had died. Soil taken from the site with seeds in the soil produced two plants, one of which flowered in cultivation in 2021. A study of this individual indicated it was a member of Schiedeasect.Mononeura, characterized by erect to ascending habit, quadrangular stems, seeds not persistent on the placenta and readily dispersing from the dehisced capsule, and flowers facultatively autogamous. With the discovery of this new species there are 35 species in this Hawaiian endemic genus.