nybg:

And so my dream of seeing a redwood as tall as the Burj Khalifa comes to a disappointing end. Still, the science behind the limitation is a pleasantly interesting consolation prize. —MN

science-junkie:

Why trees can’t grow taller than 100 metres

TYPICALLY, the taller the tree, the smaller its leaves. The mathematical explanation for this phenomenon, it turns out, also sets a limit on how tall trees can grow.

Kaare Jensen of Harvard University and Maciej Zwieniecki of the University of California, Davis, compared 1925 tree species, with leaves ranging from a few millimetres to over 1 metre long, and found that leaf size varied most in relatively short trees.

Jensen thinks the explanation lies in the plant’s circulatory system. Sugars produced in leaves diffuse through a network of tube-shaped cells called the phloem. Sugars accelerate as they move, so the bigger the leaves the faster they reach the rest of the plant. But the phloem in stems, branches and the trunk acts as a bottleneck. There comes a point when it becomes a waste of energy for leaves to grow any bigger. Tall trees hit this limit when their leaves are still small, because sugars have to move through so much trunk to get to the roots, creating a bigger bottleneck.

Jensen’s equations describing the relationship show that as trees get taller, unusually large or small leaves both cease to be viable (Physical Review Letters, doi.org/j6n). The range of leaf sizes narrows and at around 100 m tall, the upper limit matches the lower limit. Above that, it seems, trees can’t build a viable leaf. Which could explain why California’s tallest redwoods max out at 115.6 m.

Source: New Scientist.
Images: 1 - 2 - 3 - 4. 

cassieeissacsplantpages:

Hoya kerrii   ”Sweet Heart Hoya” 

So I didnt take picture of the leaves :S but they are heart shaped approx 10cm across, flowers of Hoyas are renowned for there pretty fragrance.  

(via botanicalperversion)

rhamphotheca:

Climate Change Threatens Spectacular Hawaiian Plant

by Becky Oskin

One of Hawaii’s iconic plants is again at risk.

The striking and rare Haleakalā silversword, found only on the high volcanic slopes of Maui, is on the decline, scientists report today (Jan. 15) in the journal Global Change Biology. 

First, the plant was nearly killed off by cows and collectors starting in the 1880s, then conservationists made it a success story after the 1930s. Now climate change is bringing about a new collapse.

The culprit is shifting weather patterns, which have made the plant’s environment too dry and warm for new seedlings to survive. Older plants are dying, too, said study co-author Paul Krushelnycky, a biologist at the University of Hawaii, Manoa…

(read more: Live Science)             

(photos: L -  Forest & Kim Starr via BioLib.cz; B - Paul Krushelnycky, Univ. of Hawaii at Manoa)

science-junkie:

The Sisters Olive Trees of Noah
Olea europaea

Located in Bechealeh, Lebanon, they are alleged to be the world’s oldest living olive trees (6,000–6,800 years old).
 

Sources: Wikipedia - Photos.