Adventures in "Deep Time"The First "Seed Plants" (Spermataphytes)

Author: John SibleyImage credits: John Sibley

The ferns always had a major drawback when it came to occupying the dry land, and although their dominant sporophytes have well-developed internal tubes in their stems to carry water up to their fronds, they have a reproductive “Achilles heel” in that they possess mobile sperms with lashing tails which must swim in surface water films in order to reach female fern egg cells in order to fertilise them. 

The seed plants (Spermatophytes) overcame this limitation by producing male gametes (“sex cells”) in the form of dry pollen, often carried on the wind or transported stuck to insects bodies. Apart from other fundamental structural differences seeds are generally much larger than fern spores, and contain food reserves for the growth of the young embryo plant giving them a significant advantage. This subject would demand an entire episode to explore fully! These seed design breakthroughs would see the seed plants begin to replace the spore-bearing ferns as dominant players in the Gondwanan forests of the late Permian period 250 million years ago. 

The very first seed plants may have appeared as early as the Devonian 350 million years ago, starting with the so-called “seed ferns” but it wasn’t until the late Permian/ early Triassic periods 250 million years ago that the seed plants finally came into their own with forests dominated by the now extinct Glossopteris trees towards the end of the Permian.  

Those with Northern Hemisphere links will immediately associate the term “pine tree” with long thin needles and large fist-sized pine cones (see right image).

Todays seed plants are divided into 2 main groups:
Gymnosperms = “Naked seededPinophyte Conifers with seeds exposed in cones, comprising the Pinophytes (Pines), Cycads, Ginkgos and Gnetophytes. These last three are not native to NZ but Cycads and Ginkgos are often grown in NZ gardens as introduced specimen plants. The second group of seed plants are the Angiosperms = Flowering plants with seeds hidden and enclosed within a fruit. This group includes the grasses. We will look at the Angiosperms in the next issue. 

We will look at the Gymnosperm pines or Pinophytes belonging to the Family Podocarpaceae (Podocarps) found on Tiritiri Matangi that originated from the ancient continent of Gondwana before New Zealand broke away some 80 million years ago. 

Those with Northern Hemisphere links will immediately associate the term “pine tree” with long thin needles and large fist sized pine cones – eg Pinus patula the Mexican weeping pine (see right), or Pinus radiata, the Monterrey Pine grown extensively in NZ for its timber and originating from California. 

However, in the Southern Hemisphere the dominant endemic pines are the Podocarps meaning “Foot-fruit” referring to the way the naked seed sits on top of a round fleshy “fruit” called an Aril. 

This is how the female cones of the two families of pines compare: 

Left image: Family PinaceaeRight image: Family Podocarpaceae

Look out for the Kahikatea trees Dacrycarpus dacrydioides growing in the damp stream bed of the Nikau grove. The largest one produced fruit for the first time in 2022. 

Kahikatea can grow to a height of 55 meters with a trunk exceeding 1 meter in diameter, and is New Zealand’s tallest tree species, even beating the mighty Kauri. It prefers to grow in damp swampy conditions and often lines riverbanks and other wet areas. In immature trees, the leaves are about 8mm long and lie in a flat plane along the twigs (see picture left). When mature the leaves are scale-like and are 1-2 mm long. (below left) The cone scales swell to form a red fleshy aril with the seed on top about 5mm in diameter. Birds like pigeons find them irresistible and eat them dispersing the seeds as they do so. The largest tree in the Nīkau Grove (along the Wattle Track) produced about 100 arils in 2022 which were eaten very quickly as soon as they ripened. I was lucky to catch just one to photograph! Kahikatea are often referred to as “white pine” due to its clean white timber. It imparts no flavour to food and was used to make butter boxes for export to the UK up to the middle of the 20th century. There are still a few old-growth remnants of kahikatea left in the Waikato.pastedGraphic.png

Māori used it for carving waka and for making bird spears. Its length meant it was used widely for shipbuilding, but it is not as resistant to rot as tōtara. Only 2% of the pre-European kahikatea forest remains.

Kahikatea fleshy aril and seed

The Tōtara Podocarpus totara is found in several places on Tiritiri Matangi, especially on the Tōtara, Kawerau and Ridge Tracks. Look out for the characteristic brown stringy bark and bunches of stiff and leathery leaves 20 mm long NOT on a flat plane on its twigs like the kahikatea, but protruding in all directions. 

Tōtara “cones” have two to four fused, fleshy, berry-like, juicy aril scales, bright red when mature. The cone contains one or two rounded seeds at the end of the aril scales. Tōtara can grow to 35m and its timber is favoured by Māori for large carvings, whare frames and waka building. The inner bark was used for roofing and for storage containers and the outer bark as splints to support fractured bones. 

Some of the larger canoes carved from a single tree could hold up to 100 warriors. Natural oils in the timber slow down rotting. When Europeans arrived in New Zealand, huge areas of tōtara were felled to supply general building timber, railway sleepers, bridge and wharf timbers and telephone poles. The red arils are an important food source for both humans and birds, especially tūī. Tōtara wood is very tough and can be used to produce fire by friction where a pointed stick is scraped on a slab of softer wood such as māhoe and a glowing ember created.

Tōtara is found in several places on Tiritiri Matangi.

Which animals found on Tiritiri Matangi today would have appeared around this time 250 million years ago alongside these trees? 

The wētās belong to the Insect Order Orthoptera (meaning “straight wings”) alongside the locusts, grasshoppers and crickets. There are three species present on Tiritiri Matangi, the giant wētā (Deinacrida heteracantha), the ground wētā (Hemiandrus sp) and the Auckland tree wētā (Hemideina). 

The female giant wētā can achieve a weight of 70 grams making it one of the heaviest insects in the world. All insects rely on an air-filled tracheal tube system to deliver oxygen to their internal tissues and remove carbon dioxide. This is not a very efficient means of gas exchange, and it limits the maximum size an insect can grow to. Our giant wētā are right on that limit. Consequently, they spend much of their time sitting motionless – a good way to avoid being eaten by a passing tīeke. When they do have to move, they can do so quite rapidly but for a short time only before having to rest and recover. 

There are eleven species of deinacrida giant wētā in New Zealand, mostly restricted to mammal-free islands. On Tiritiri Matangi we have the Little Barrier giant wētā Deinacrida heteracantha translocated here in 2014. At one time this species was widespread from Northland to Auckland. It probably reached Tiritiri Matangi and Hauturu during the last Ice Age 11,00 years ago when sea levels dropped and Tiritiri Matangi was a hill surrounded by forest on flat coastal plains. 

One South Island species is an Alpine specialist and is capable of recovery after being frozen solid when temperatures drop below -5 C. These wētā are good examples of island gigantism. This is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. There are several possible reasons for this, a lack of predators on isolated islands allows larger less nimble individuals to survive that would otherwise have been eaten. Larger bodies are better able to store food and maintain a constant internal temperature giving a survival advantage. Other examples in New Zealand include takahē and moa. 

The Caddisflies (right) are another ancient group of insects that appeared around this time. Caddisflies belong to the order Trichoptera (meaning ”Hairy wings”). In New Zealand, we have many freshwater species and even five species of marine caddisfly, one of which, philanisus plebeius, is present on Hobbs beach living amongst the rockpools. Adult caddisflies are poor flyers with more than a passing resemblance to small moths. Adults lay their eggs within the bodies of cushion stars where the larvae develop for a time, eventually emerging by burrowing out through the mouth of the starfish, and then building a protective case of sand grains and silk to protect and camouflage themselves. In rockpools, they graze on red encrusting coralline algae and the diatoms that live on them. They pupate amongst the seaweed and emerge as a non-feeding adult to mate and repeat the cycle. Marine insects are incredibly rare and these caddisflies are found nowhere else on Earth. 

Left image: Wētāpunga matingMiddle image: CaddisfliesRight image: Caddisflies larvae