The Most Southerly Oaks in the World

What a cliff hanger I left you with three weeks ago (as the lads on The Rest is History podcast are wont to say). Not in the Americas, but someone on our planet, I wrote, oaks crossed the equator (southward) without our help. 

But before I tell you where, let's start at the top. Literally. 

Japanese Blue Oak (Quercus glauca), widespread in continental Asia; Royal Botanic Gardens Melbourne, February 2024

There are 100 peaks in the Himalaya range rising 7,200 metres or more above sea level, and perhaps not unexpectedly, you won’t find any oaks at those altitudes. Not even around the base camps for Mount Everest which are closer to 5,000 metres. 

Drop a little further though, and oaks are some of the first trees you’ll encounter. They are mostly relatives of the holly (or holm) oaks from the Mediterranean (subgenus Cerris, section Ilex). That group, or clade, of oaks actually evolved in the foothills of the Himalaya then moved westward to Europe.

These 'Holly Oaks' cling to slopes around 4,200 metres, where they withstand winter temperatures as low as –22˚C and wind speeds I can only imagine. No 'Cycle-cup' (subgenus Cerris, section Cyclobalanopsis) or 'White Oaks' (subgenus Quercus, section Quercus) are found here, but they come into their own once you drop below 3,000 m. 

Leaves of the above

As you head south, the 'White Oaks', 'Holly Oaks' and even a few 'Cork Oaks' (subgenus Cerris, section Cerris) peter out in the northern parts of Myanmar, Vietnam, Laos, Thailand and Cambodia, leaving only 'Cycle-cup Oaks' by the time you get to Malaysia.

The only true oaks (genus Quercus) in Malesia are 'Cycle-cup Oaks'. The diversity varies across the region. The whole of Malaysia has some 19 native species, while the Philippines has only one, Merrill's Oak (Quercus merrillii), a two metre high shrub growing in dipterocarp forests on the western island of Palawan. Merrill's oak also grows in the Malaysian states of Sarawak and Sabah on Borneo.

Borneo in its entirety, is home to 18 oak species, most of these again in the Malaysian part and therefore north of the equator. The protected forests around Mount Kinabalu are particularly rich in oak species, with at least ten recorded from the Kinabalu massif, and three of those only found there.  

Leaves of the jolcham oak (Quercus serrata), from eastern continental Asia; Royal Botanic Gardens Melbourne, February 2024

But here's the exciting bit if, like me, you were left in suspense when I reported on the shock news that oaks in the Americas get to within one degree north of the equator but no further south. I am delighted to announce here that in Indonesia, at least five native species of oak cross the equator into the Southern Hemisphere. 

While oak diversity drops as you move south - particularly the south-east, with Sulawesi and Maluku having no true oaks (they do have what are called stone oaks, species of Lithocarpus) - oaks persist on the western islands.

Fruit of Wu Huan Qing Gang (Quercus oxyodon) from southern China and northern Vietnam; Royal Botanic Gardens Melbourne, April 2024

The island of Java at a latitude of 7 to 8 degrees South, has five species of oak. These include the ear-fruited oak (Quercus oidocarpa), which grows from Thailand through Malayasia to Borneo and then the Javan islands. Despite the botanical name – which I’ve coarsely converted into a common name, sorry – the acorns and cups are not unusual for a Cycle-cup Oak. Also, the Asian silky oak (Quercus subsericea; not to be confused with the Australian silky oak, Grevillea robusta!), also from Borneo and Malay Peninsula, and the narrow-leaved oak (Quercus lineata), which can be found all the way to Assam, in India. It has moderately narrow leaves for a 'Cycle-cup Oak' but not unusually so. 

To my eye, these most southerly of oaks are not the most interesting in form, although attractive enough, particularly some of the finely honed acorn cup rings. They are all widespread Malesian species that haven’t had the time – or inclination – to become new species since arriving in the Southern Hemisphere. 

Leaves of the above

Note: Because none of the Javan species grow, or would likely be able to grow well, in Royal Botanic Gardens Melbourne, and I have not visited Java itself, I have no pictures of oaks from there. Instead, I've illustrated this post with a few mainland Asian 'Cycle-cup Oaks' growing in Royal Botanic Gardens Melbourne. A reminder of the general form of 'Cycle-cup Oaks'.