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.