Data from: Insular woody daisies (Argyranthemum , Asteraceae) are more resistant to drought-induced hydraulic failure than their herbaceous relatives

1. Insular woodiness refers to the evolutionary transition from herbaceousness towards derived woodiness on (sub)tropical islands, and leads to island floras that have a higher proportion of woody species compared to floras of nearby continents. 2. Several hypotheses have tried to explain insular woodiness since Darwin’s original observations, but experimental evidence why plants became woody on islands is scarce at best. 3. Here, we combine experimental measurements of hydraulic failure in stems (as a proxy for drought stress resistance) with stem anatomical observations in the daisy lineage (Asteraceae), including insular woody Argyranthemum species from the Canary Islands and their herbaceous continental relatives. 4. Our results show that stems of insular woody daisies are more resistant to drought-induced hydraulic failure than the stems of their herbaceous counterparts. The anatomical character that best predicts variation in embolism resistance is intervessel pit membrane thickness (TPM), which can be functionally linked with air bubble dynamics throughout the 3D vessel network. There is also a strong link between TPM vs degree of woodiness and thickness of the xylem fiber wall vs embolism resistance, resulting in an indirect link between lignification and resistance to embolism formation. 5. Thicker intervessel pit membranes in Argyranthemum functionally explain why this insular woody genus is more embolism resistant to drought-induced failure compared to the herbaceous relatives from which it has evolved, but additional data are needed to confirm that palaeoclimatic drought conditions has triggered wood formation in this daisy lineage.

1. 岛屿木质化（insular woodiness）指的是（亚）热带岛屿上植物从草本习性向进化衍生的木质化习性的演化过渡，其结果是相较于邻近大陆的植物区系，岛屿植物区系拥有更高比例的木本物种。2. 自达尔文最初的观察以来，已有多项假说试图解释岛屿木质化现象，但迄今为止能够解释植物为何在岛屿上演化出木质化特性的实验证据仍极为匮乏。3. 本研究将茎部水力衰竭（作为抗旱性的替代指标）的实验测量结果，与菊科（Asteraceae）雏菊类演化支的茎部解剖学观测相结合，研究对象包括来自加那利群岛的岛屿木质化木茼蒿（Argyranthemum）物种及其草本的大陆近缘类群。4. 本研究结果显示，岛屿木质化雏菊类的茎部相较于其草本近缘类群，对干旱诱导的水力衰竭具有更强的抗性。最能预测抗栓塞性变异的解剖学特征为导管间纹孔膜厚度（TPM），该特征可与三维导管网络内的气泡动力学建立功能关联。此外，导管间纹孔膜厚度与木质化程度、木质部纤维细胞壁厚度与抗栓塞性之间均存在显著关联，进而使木质化作用与抗栓塞形成抗性之间形成间接关联。5. 木茼蒿属植物更厚的导管间纹孔膜，从功能上解释了该岛屿木质化类群相较于其演化起源的草本近缘类群，为何对干旱诱导的栓塞衰竭具有更强的抗性，但仍需额外的数据来证实古气候干旱条件曾触发该雏菊类演化支的木质化形成。