American Journal of Botany最新文献

{"title":"Geographic isolation promoted species divergence of two closely related Cycas species in distinct river basins.","authors":"Yi-Qing Wang, Jian Liu, Si-Yue Xiao, Hui-Hui Xi, Xun Gong, Xiu-Yan Feng","doi":"10.1002/ajb2.70270","DOIUrl":"https://doi.org/10.1002/ajb2.70270","url":null,"abstract":"<p><strong>Premise: </strong>Understanding the process of species divergence and the mechanisms that drive genetic differentiation among closely related species is essential for explaining the origins of plant biodiversity. Geographic isolation and niche differentiation are key drivers of species divergence. Cycas chenii and C. guizhouensis are morphologically similar sister species from different river basins in Southwest China. Their distinct habitats in nearby river systems make them a potentially good model system for studying species divergence.</p><p><strong>Methods: </strong>We used double-digest restriction-site-associated DNA sequencing data and analyzed the data with a range of analyses to investigate the genetic divergence of C. guizhouensis and C. chenii and to assess the significance of geographic factors and ecological differentiation in their divergence.</p><p><strong>Results: </strong>The two species had significant genetic differentiation (genetic differentiation index = 0.34). On the basis of phylogenetic and admixture analyses, the two species are genetically distinct lineages that diverged in the early Miocene. They experienced similar demographic histories over the past several million years. The genetic distance between the two species correlated positively with geographic distance but not with environmental distance. In a niche identity test, the ecological niches of the two species were statistically indistinguishable (Schoener's D = 0.68, I = 0.91, both within the null distribution).</p><p><strong>Conclusions: </strong>Environmental variation is unlikely to have been the primary factor driving divergence of C. chenii and C. guizhouensis. Geographic separation instead may have been triggered by shifts in river channels during the early Miocene epoch, playing a pivotal role in interspecific differentiation.</p>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":" ","pages":"e70270"},"PeriodicalIF":2.8,"publicationDate":"2026-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149079479","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Bird pollination in three species of Phlogacanthus and its broader implications for bird–flower interactions in Asia","authors":"Chang-Qiu Liu,&nbsp;Li-Yan Wang,&nbsp;Ying-Ze Xiong,&nbsp;Zhe Chen,&nbsp;Wenyi Zhou,&nbsp;Li-Ping Zhou,&nbsp;Yang Niu,&nbsp;Yun-Dong Gao,&nbsp;Yan-Qiong Peng,&nbsp;Qiang-Bang Gong","doi":"10.1002/ajb2.70261","DOIUrl":"10.1002/ajb2.70261","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>Our knowledge of bird–flower interactions in Asia is limited. Here, we investigated the pollination ecology of three <i>Phlogacanthus</i> species that differ substantially in floral tube length. The floral tubes of bird-pollinated flowers may either correspond to the bill length of the primary bird pollinator, or relatively short-tubed flowers may be pollinated by both short- and relatively long-billed birds. The pollination systems of the three <i>Phlogacanthus</i> species may differ in traits other than floral tube length, reflecting their association with different bird groups.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>We observed floral visitors at multiple sites over multiple years and compared pollination effectiveness and foraging behavior between bird visitors. We also measured floral traits, including corolla morphology and color and nectar quality and quantity.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>The short-, medium-, and long-tubed <i>Phlogacanthus</i> species were mainly or solely pollinated by short-, medium-, and long-billed birds, respectively. The visitor assemblage of the short-flowered species varied considerably with the population in terms of bird species, genus, or family relative to those of the other two <i>Phlogacanthus</i> species. Sunbirds and spiderhunters occasionally hovered to extract nectar. The floral height of the inflorescence determined whether the birds hovered or perched. Although all three <i>Phlogacanthus</i> species are bird-pollinated, they also differ in their nectar and floral morphological traits. These differences likely reflect additional adaptations to distinct bird groups.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>The three Phlogacanthus species represent distinct pollination systems connected to the three bird-pollination niches in Asia. Our study provides novel natural historical details associated with bird–flower interactions in Asia.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148981997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Austrocedrus from the Late Cretaceous of Antarctica and its implications for the early evolution of southern cypresses (Callitroideae, Cupressaceae)","authors":"Kelly C. Pfeiler,&nbsp;Kelly K. S. Matsunaga,&nbsp;Ana Andruchow-Colombo,&nbsp;Ari Iglesias,&nbsp;Selena Y. Smith,&nbsp;Brian A. Atkinson","doi":"10.1002/ajb2.70253","DOIUrl":"10.1002/ajb2.70253","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>The modern distribution of the southern cypresses, Callitroideae (Cupressaceae), reflects a classic Gondwanan distribution. The initial diversification of Callitroideae is estimated to have occurred during the Cretaceous, yet fossils from this period are rare, hampering our understanding of its early evolutionary history.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>A permineralized cluster of callitroid seed cones has been recovered from the Late Cretaceous Santa Marta Formation on James Ross Island, Antarctica. The specimen was sectioned using the acetate peel technique. We conducted a comparative morphological and anatomical investigation of the fossil with living members of Callitroideae and tested its phylogenetic placement using Bayesian and parsimony inference methods.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Each cone has four opposite-decussate ovuliferous complexes, a central columella, and subtending bifacially flattened shoots. This new fossil resembles living <i>Austrocedrus</i> in having ovuliferous complexes with a short, apically located bract tip and an abaxial row of vascular bundles. Phylogenetic reconstructions place the fossil sister to <i>Austrocedrus chilensis</i>, and we erect a new species, <i>Austrocedrus vetus</i> sp. nov.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p><i>Austrocedrus</i> is known by a handful of Cenozoic fossils from Australia and a single surviving taxon, <i>A. chilensis</i>, in the Southern Andes of Chile and Argentina. <i>Austrocedrus vetus</i> is the oldest evidence of the genus, extending its stratigraphic record by 40 Ma. Our findings indicate that <i>Austrocedrus</i> diverged by the Campanian and experienced stasis in seed cone morphology. Furthermore, this fossil is the first occurrence of <i>Austrocedrus</i> in Antarctica, demonstrating that the genus was an element of Antarctic forest ecosystems during the Late Cretaceous.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajb2.70253","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148918019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"At the edge of change: Native Phragmites persistence and nonnative arrival along the dam-regulated Colorado River","authors":"Emily C. Palmquist,&nbsp;Joel B. Sankey,&nbsp;Claudia DiMartini,&nbsp;Tayan Benson,&nbsp;Brooke Damon,&nbsp;Helen Fairley,&nbsp;Bradley J. Butterfield","doi":"10.1002/ajb2.70258","DOIUrl":"10.1002/ajb2.70258","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>The southwestern United States is at the forefront of nonnative <i>Phragmites australis</i> subsp. <i>australis</i> expansion. Native <i>Phragmites australis</i> subsp. <i>americanus</i>, likely in decline in North America, is ecologically and culturally important and of conservation interest. In the greater Grand Canyon region, the Glen Canyon Dam led to loss of habitat upstream and increases in <i>Phragmites</i> downstream. Recent increases correspond with changes to dam operations and the arrival of nonnative <i>Phragmites</i>. Determining the native status of <i>Phragmites</i> stands along the Colorado River and around Lake Powell can inform complex management choices and restoration planning.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p><i>Phragmites</i> subspecies at 83 locations from southern Utah through northern Arizona, United States were genetically tested using real-time PCR. Genetic diversity and structure were assessed using microsatellite loci for 13 native <i>Phragmites</i> stands. Morphological traits of southwestern native <i>Phragmites</i> were compared to those of nonnative <i>Phragmites</i>.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Nonnative <i>Phragmites</i> was identified at four of the 83 locations. Native <i>Phragmites</i> in the study area is genetically diverse with little regional genetic structure, but substantial genetic differentiation among sites. Southwestern native <i>Phragmites</i> is morphologically variable, but characteristics can be used together to distinguish it from nonnative <i>Phragmites</i>.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>The greater Grand Canyon and Glen Canyon regions support a large, genetically diverse native <i>Phragmites</i> population, which is potentially threatened by nonnative <i>Phragmites</i> and changes to river management. Determining conditions that would lead to nonnative <i>Phragmites</i> invasion of desert wetlands will facilitate discussions about the risks and benefits of <i>Phragmites</i> management in these unique ecosystems.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajb2.70258","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148962774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Resolving the “Yucca queretaroensis problem”: Phylogenomic analysis of Yucca reveals the identity of an enigmatic species and the origin of an obligate pollination mutualism","authors":"Christopher Irwin Smith,&nbsp;Erika Aguirre Planter,&nbsp;Marian Angeles-Cruz,&nbsp;Ramona Flatz,&nbsp;Abisaí García-Mendoza,&nbsp;Jaime Gasca-Pineda,&nbsp;Emma Fabiola Magallán-Hernández,&nbsp;Guillermo Sánchez-de la Vega,&nbsp;Emelia Sherman,&nbsp;Cécile Truchot Taillefer,&nbsp;Luis E. Eguiarte","doi":"10.1002/ajb2.70259","DOIUrl":"10.1002/ajb2.70259","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>The genus <i>Yucca</i> is a group of ~50 species of woody monocots endemic to the North American arid regions. Their obligate pollination mutualism with yucca moths is considered a “textbook example” of coevolution and is hypothesized to have promoted rapid diversification. However, testing this hypothesis has been difficult due to uncertainty about the placement of a rogue taxon, <i>Yucca queretaroensis</i>, a rare endemic of the Sierra Gorda region of central Mexico. Past work placed this species in different positions within the Agavoideae, producing starkly different age estimates for <i>Yucca</i> (25 to 4 million years).</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>We generated new sequence capture data for 353 nuclear genes and for all coding regions of the plastid genome from wild-collected plants and samples included in previous studies to provide a new phylogeny and new age estimate for <i>Yucca</i>.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>The data presented here suggest that <i>Y. queretaroensis</i> is closely related to other species of <i>Yucca</i>. A relaxed molecular clock analysis of the plastid genome produced an estimated age for the genus of approximately 6.8 million years.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>The results resolve a mystery that has bedeviled evolutionary biologists for decades and provide a surprisingly young estimate for the age of <i>Yucca</i>, suggesting rapid diversification. The past difficulties in identifying the correct placement of <i>Y. queretaroensis</i> appear to be the product of laboratory errors, mistakes in field identification, and frequent hybridization with co-distributed taxa. The “<i>Yucca queretaroensis</i> problem” reaffirms the essential role for traditional botanical tools in phylogenomics.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148917980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ferns, marsupials, and Darwin's Wedge: Does competitive displacement really explain macroevolutionary patterns in ferns?","authors":"Jacob S. Suissa","doi":"10.1002/ajb2.70266","DOIUrl":"10.1002/ajb2.70266","url":null,"abstract":"&lt;p&gt;Darwin's metaphors are palpable. The tangled bank, struggle for existence, and tree of life command comprehension of his arguments. One of his most profound metaphors is the likening of competition to a “yielding surface, with ten thousand sharp wedges” (Darwin, &lt;span&gt;1859&lt;/span&gt;, p. 67). In this metaphor, nature (the surface) is overly crowded with species (the wedges). As one wedge is struck, others are affected to varying degrees; and one will survive only if another is directly outcompeted. In this scenario, natural selection is the hammer that strikes the wedge—a driver of new adaptations that allow some species to conquer others. While competition between individuals of the &lt;i&gt;same species&lt;/i&gt; is ubiquitous, this metaphor for competitive displacement &lt;i&gt;between species&lt;/i&gt; is often invoked to describe long-term evolutionary trends between lineages (Strotz and Lieberman, &lt;span&gt;2023&lt;/span&gt;).&lt;/p&gt;&lt;p&gt;In the narrative of evolutionary history, there are certain lineages to which we hand the short end of the proverbial stick—or the loose wedge on the surface. American marsupials are among the examples that come to mind (Marshall et al., &lt;span&gt;1982&lt;/span&gt;). Their story follows that during the Great American Biotic Interchange (GABI) northern placental mammals outcompeted the South American marsupials due to their superior reproduction and a slew of other adaptations. It is a tale of conquest through competition (Gould, &lt;span&gt;1983&lt;/span&gt;). The time period of the GABI was surely impactful on South America, as roughly half of its extant fauna is North American in origin and, many southern forms went extinct around this time (Carrillo et al., &lt;span&gt;2020&lt;/span&gt;). But does the decline of South American marsupials inherently imply that they were directly outcompeted and displaced?&lt;/p&gt;&lt;p&gt;Not necessarily.&lt;/p&gt;&lt;p&gt;Macroevolutionary trends showing the decline of one lineage and rise of another are often used as evidence for competitive displacement—a lineage replacing another in an environment, through direct competition (Sepkoski, &lt;span&gt;1996&lt;/span&gt;). With a reference to Darwin's “wedge,” Sepkoski (earlier [Benton, &lt;span&gt;1987&lt;/span&gt;]) describes this macroevolutionary pattern as a “double wedge” since it looks like two tip-to-tip wedges in a lineage through time plot. However, these patterns do not &lt;i&gt;intrinsically&lt;/i&gt; imply competition occurred (Gould and Calloway, &lt;span&gt;1980&lt;/span&gt;; Simberloff, &lt;span&gt;1984&lt;/span&gt;; Lidgard et al., &lt;span&gt;2021&lt;/span&gt;); indeed in 1987 Benton explains that even if “a ‘double-wedge’ pattern is demonstrated in the fossil record, it could be a chance association of two taxa that never interacted.” Even between living taxa, confirming competitive processes remains quite difficult (Harper, &lt;span&gt;1977&lt;/span&gt;; Vorburger and Ribi, &lt;span&gt;1999&lt;/span&gt;; Harpole and Tilman, &lt;span&gt;2007&lt;/span&gt;; Sakarchi and Germain, &lt;span&gt;2023&lt;/span&gt;); a difficulty that is compounded when trying to attribute causal ecological processes to correlative time series","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajb2.70266","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148981992","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Incomplete climate-driven peripatric speciation in Moehringia sect. Moehringia (Caryophyllaceae) in the European Alps","authors":"Joachim W. Kadereit,&nbsp;Kirra McLeod,&nbsp;Audie M. Putra,&nbsp;Gudrun Kadereit,&nbsp;Diego F. Morales-Briones","doi":"10.1002/ajb2.70252","DOIUrl":"10.1002/ajb2.70252","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>The origin of endemic species in the European Alps is commonly attributed to the climatic oscillations of the Quaternary. <i>Moehringia</i> sect. <i>Moehringia</i>, with 12 of 15 species endemic to the Alps and mostly restricted to well-known glacial refugia, is a prime system for investigating the diversification of a lineage originating in the Alps.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>We used all species in this lineage, most of which were represented by multiple accessions, and a target enrichment approach with baits specifically designed for <i>Moehringia</i> to obtain a phylogenetic tree from 829 nuclear loci. We also dated the phylogenetic tree with a molecular clock approach.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Most species originated in the Quaternary. Four regionally distributed species (<i>M. intermedia</i>, <i>M. markgrafii</i>, <i>M. papulosa</i>, <i>M. tommasinii</i>), all nested within the widespread <i>M. muscosa</i>, were found to be between 1.36 and 0.25 million years old. <i>Moehringia muscosa</i> and the four species derived from it differ in habitat, leaf succulence, and glaucousness.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>Because the widespread species has not coalesced into monophyly and the regionally distributed species have evolved in glacial refugia, we consider speciation in this lineage incomplete and climate-driven. Divergence in habitat and leaf morphology between the widespread and the derived species suggests a role of adaptive evolution.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajb2.70252","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148823469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Humidity and temperature interact in breaking physical dormancy in Fabaceae seeds from the Brazilian semiarid region","authors":"Humberto Araújo Almeida,&nbsp;Jessyca Adelle Silva Santos,&nbsp;Queila Souza Garcia","doi":"10.1002/ajb2.70254","DOIUrl":"10.1002/ajb2.70254","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>In semiarid ecosystems such as the Brazilian Caatinga, physical seed dormancy (PY) is critical for plant persistence when water is unpredictable, but how soil moisture and temperature regulate PY release and seed longevity in species of native Fabaceae that have different growth forms is unknown.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>Seeds of the herbaceous species <i>Centrosema pascuorum</i> and <i>Crotalaria retusa</i> and tree species <i>Mimosa ophthalmocentra</i>, <i>M. tenuiflora</i>, and <i>Piptadenia retusa</i> were collected in the Caatinga and tested in the field and laboratory to assess dormancy, viability, and germination. Seeds were either buried at the collection site and periodically exhumed over 15 months, or stored dry or with wet–dry cycles at constant or fluctuating temperatures.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Seeds of herbaceous species had rapid PY release and seed depletion shortly after the onset of rainfall, leading to synchronized seedling emergence. Seeds of the trees <i>M. ophthalmocentra</i> and <i>M. tenuiflora</i> maintained high dormancy and viability, indicating strong potential for persistent soil seed banks, whereas seeds of <i>Piptadenia retusa</i> had low persistence due to rapid dormancy loss and high mortality. Across species, PY release was maximized under wet–dry cycles at high temperatures, revealing a synergistic effect of moisture pulses and heat.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>Temperature–moisture interactions characteristic of the Caatinga control PY release and seed persistence, with growth form shaping contrasting regeneration strategies. The delayed release of PY in trees spreads germination over time, enhancing persistence under unpredictable rainfall. Early PY release in herbs optimizes exploitation of short favorable windows to complete their rapid life cycle.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajb2.70254","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148890815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cellular basis for blade splitting in bull kelp, Nereocystis luetkeana","authors":"Alana K. Breitkreutz,&nbsp;Patrick T. Martone","doi":"10.1002/ajb2.70262","DOIUrl":"10.1002/ajb2.70262","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>Blade splitting in bull kelp, <i>Nereocystis luetkeana</i> is central to thallus development and function, yet the cellular basis of this process remains poorly understood. Two historical models proposed contrasting mechanisms: One attributes blade separation primarily to programmed cell death, whereas the other suggests mechanical tearing followed by tissue regeneration. Resolving the mechanism underlying blade splitting is important for understanding kelp morphogenesis and functional morphology in high-flow environments.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>We used bright-field light microscopy to examine histological sections of developing blades undergoing separation and compared their tissue structure with predictions from the two historical models. Cellular organization, tissue thickness, and evidence of cell death and recovery were assessed during successive stages of blade separation.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>We found no evidence of programmed cell death associated with blade division. Instead, blade splitting proceeds through a developmental sequence involving localized tissue thinning, mechanical tearing, and rapid healing. Thinning occurs without a loss of cells, indicating reduced extracellular matrix rather than cell death. Following mechanical tearing of the blade tissue, newly exposed blade margins rapidly undergo cell proliferation to regenerate new blade surfaces. Comparisons of this process to sorus detachment in this species, which involves programmed cell death, further demonstrate that blade splitting operates through a distinct physiological pathway.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>Blade splitting in <i>Nereocystis</i> is driven by mechanical tearing facilitated by localized reductions in blade thickness rather than programmed cell death. By subtly modifying tissue geometry, developing blades harness hydrodynamic forces to direct tearing and thereby produce streamlined morphologies and extensive habitat in hydrodynamically stressful environments.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajb2.70262","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148910679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Untangling the Arisaema enigma: Investigating the complex evolutionary history and species relationships in North American Arisaema","authors":"Luka Sato,&nbsp;Robert Wyatt,&nbsp;Ann Stoneburner,&nbsp;Rebecca Y. Kartzinel,&nbsp;Brock Mashburn,&nbsp;Christine E. Edwards","doi":"10.1002/ajb2.70260","DOIUrl":"10.1002/ajb2.70260","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Premise</h3>\u0000 \u0000 <p>The evolutionary history of morphologically variable plant groups is often obscured by cryptic diversity, morphological convergence, and limited genetic data. <i>Arisaema</i>, a diverse genus within Araceae, exemplifies these challenges. Although some taxonomic treatments recognize only two species of North American <i>Arisaema</i> (<i>A. dracontium</i> and <i>A. triphyllum</i>), other studies have identified morphologically distinct groups within both taxa. Here, we reconstructed evolutionary relationships in North American <i>Arisaema</i>, assessed genetic structure and admixture, and tested the monophyly of proposed species.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>We used 2b-RAD sequencing to generate genome-wide SNP data for 146 samples from 31 populations across the eastern United States. Phylogenetic relationships were inferred using maximum-likelihood and Bayesian approaches. Population structure and admixture were assessed using the program <span>structure</span> and principal component analysis (PCA).</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Both the <i>Arisaema triphyllum</i> and <i>A. dracontium</i> complexes formed well-supported monophyletic groups. Within the <i>A. dracontium</i> complex, we recovered three monophyletic lineages: <i>A. dracontium</i>, <i>A. calciphilum</i>, and <i>A. macrospathum</i>. In the <i>A. triphyllum</i> complex, <i>A. quinatum</i>, <i>A. stewardsonii</i>, and <i>A. allegheniense</i> consistently formed distinct groups. Relationships between <i>A. pusillum</i> and <i>A. acuminatum</i>, and among <i>A. triphyllum</i> s.s., <i>A. purpurascens</i>, and <i>A. striatum</i> were less clearly resolved, likely due to recent or incomplete divergence, gene flow, or polyploidy.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>The results support the monophyly of multiple newly proposed taxa within North American <i>Arisaema</i>, but additional sampling across the species' ranges is needed to fully resolve species boundaries. Our study provides the first evolutionary framework for this group, providing a foundation for future ecological, taxonomic, and conservation research in the genus.</p>\u0000 </section>\u0000 </div>","PeriodicalId":7691,"journal":{"name":"American Journal of Botany","volume":"113 9","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148966156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}