Abstract Detail

Ecophysiology

Chatelet, David [1], Sack, Lawren [2], Scoffoni, Christine [2], Edwards, Erika J. [3], Donoghue, Michael [4].

The evolution of stem anatomy in Viburnum (Adoxaceae) and its significance for plant function.

Viburnum is a clade of ~165 species of shrubs and trees that occupy mainly temperate (but also some tropical) mesic forests, primarily around the Northern Hemisphere. In connection with our ongoing studies of leaf form and hydraulics, branching architecture, and diversification dynamics, we surveyed 103 species for a set of wood anatomical characters. This revealed remarkable structural conservatism across the entire clade (spanning tropical to temperate environments), but also phylogenetically and functionally important diversity. Viburnum clemensiae, from Borneo (the sister species of the rest of Viburnum) has a low vessel density of ~90 mm^-2, with relatively long (~1240 um) and wide (~32 um) vessels elements, and elongate perforation plates (~340 um) with multiple scalariform bars (~88). In marked contrast, V. integrifolium from Taiwan has a high vessel density of ~530 mm^-2, with shorter (~500 um) and narrower (~19 um) elements, and shorter perforation plates (~80 um) with few scalariform bars (~2). We found that two early-diverging (but distantly related) species from tropical forests in Borneo, V. clemensiae and V. amplificatum, were strikingly similar in their vessel elements. Concordant with their phylogenetic positions, and several other shared characteristics, we interpret their vessel elements as ancestral in Viburnum, having probably been retained along the entire Campanulidae backbone. We note, however, that several other tropical species from Southeast Asia, in the Sambucina clade, differ considerably from V. clemensiae and V. amplificatum, and from one another. For example, V. beccarii, a liana from Peninsular Malaysia, has a vessel density of ~205 mm^-2, with vessel elements of ~1473 um in length, and perforation plates of 381 um with 54 bars, whereas V. vernicosum from Borneo, has a vessel density of ~781 mm^-2, with vessel elements of ~759 um in length, and perforation plates of 121 um with 24 bars. The Valvatotinus clade stands out as having consistently shorter vessel elements (~760 um on average, vs. ~930 um in all other viburnums), shorter perforation plates (112 um vs. 211 um), and fewer bars (24 vs. 50). Interestingly, the Valvatotinus clade also shows, on average, higher leaf hydraulic conductivity (Kleaf), higher maximum photosynthetic capacity (Amax), and thicker leaves with palisade layers of elongated I-cells. Other aspects of stem anatomy are noteworthy, especially the production in the Amplicrenotinus clade of a continuous cylinder of thick walled sclerids in the cortex, which might protect the phloem from specialized insect larvae.

1 - Yale University, Ecology and Evolutionary Biology, 21 Sachem street, New Haven, CT, 10620, USA
2 - UCLA, 621 Charles E. Young Drive South, Los Angeles, CA, 90095, USA
3 - Brown University, Box G-W, 80 Waterman St, Providence, RI, 02912, USA
4 - Yale University, Department Of Ecology And Evolutionary Biology, 21 Sachem Street, PO Box 208105, New Haven, CT, 06511, USA

Keywords:
Viburnum
Evolution
stem anatomy
xylem
plant function.

Presentation Type: Oral Paper:Papers for Topics
Session: 25
Location: Salon 16/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 9:00 AM
Number: 25005
Abstract ID:1311
Candidate for Awards:None