In 2005 we moved onto a bush block on the South Coast of New South Wales, Australia. There were quite a few ferns on our block, and this is what led to us to start collecting them. Around 2007, we started operating our fern nursery as a way to expand our collection. This may possibly have grown into a bit of an obsession over the years. Our stock plants were all kept in the nursery, and we would get plenty of volunteers popping up here and there with all the spore floating around.
Anything that looked different, we would put aside. Over the years, we ended up with quite a few oddballs—things that didn’t really match the species we had but looked similar. Quite a few of these looked like Blechnum or Doodia. Of course, Blechnum has been split into different genera, but for the purposes of simplicity I’m going to use the old genus name.
Skip forward a decade plus some and we had come to the conclusion that most of these oddballs were probably hybrids. Most looked a bit like Doodia aspera, a common native in our area. We had two different forms of Doodia maxima which also seemed to fit in this group of oddballs. We’d never seen any of these in nature, despite 15 years of treks into the bush. A bit of cresting here and there, but no hybrids. And this is where the irony kicks in.
Early this year, we were doing a bit of gardening on the top of our block. There was this patch of ferns I’d mowed around for years. They were in a slight depression about 1 m across and more than once I’d considered mowing them as well (Figure 1). From a distance, they just looked like Blechnum cartilagineum (now Oceanopteris cartilaginea, not to be confused with the separate taxa Blechnum occidentale from Mexico and
the South Americas which also has Blechnum cartilagineum as a synonym). But as I was walking past this patch on the way to where we were gardening, I noticed the spore pattern clearly indicated a hybrid (Figure 2). Certainly not what I’d expected to see! At this point, I had a bit of a laugh. I’d been searching for a hybrid for ages and I had been walking past one a few times a week for years without even noticing. The patch is about 20 m from my front door and both parents naturally occur within 10 m of the patch (Figure 3).
Now, let’s revisit D. maxima. There has been speculation that this is a naturally occurring cross between D. aspera and B. cartilagineum. If this is true, then the
patch on my block is also a D. maxima, which makes at least three variant
hybrids. I’ll get back to this a little later.
So, onto the technical stuff, courtesy of Peter Hind from our local fern
study group in New South Wales.
Doodia maxima = Blechnum cartilagineum × Doodia aspera
I have no doubt that plants ascribed to this taxon (D. maxima) are unrelated to each other being an assemblage of separate, potentially sterile, clones. The result of a recurring natural hybrid between B. cartilagineum and D. aspera, is based on the observable morphological characteristics inherited from the purported parents.
Most plants are closer in appearance to B. cartilagineum, the fertile fronds being narrower than the sterile fronds. The plants that look closer to D. aspera, have a harsh sandpaper texture and are more or less not dimorphic. They have pale green fronds with the lowermost pinnule pair occasionally deflexed, these last two characters are derived from B. cartilagineum. The sori in all are like D. aspera, but are in a single row each side of and close to the pinnule midrib, rarely a few in a second row.
The herbarium material, including Charles Fraser’s collection from the Warragamba River in 1825 held at Kew, consist of fertile fronds only. Herbarium specimens from Queensland and New South Wales, held at Brisbane and Sydney, show its range as being from Noosa Heads, Queensland to Lawlers Creek, West of Dalmeny on the South
Coast of New South Wales. Anecdotal reports suggest that D. maxima is sterile. Each clone needs to be tested, although if fertile you would expect to find larger unconnected colonies.
A new occurrence of this taxon has recently been discovered by Dwayne Stocks at Currowan Creek, west of Batemans Bay, New South Wales. It consists of one patch of interconnected plants. The sterile fronds have much wider pinnules than the fertile ones, much like many plants of B. cartilagineum (B. cartilagineum and D. aspera are both abundant at this site) (Figure 4). This clone besides being noticeably dimorphic has quite a distinctive sori pattern, with at least some of the pinnules having a second row of sori, alternating with the ones close to the midrib, coalescing as they ripen. The large fronds of D. aspera often have two rows of sori (Figure 5 and Figure 6). The deflexed lowermost pinnule pairs on the sterile fronds are particularly noticeable. As in
B. cartilagineum, they point backwards forming an acute angle with the upper surface of the stipe (Figure 7). The basal stipe scales are fairly long and resemble those of B. cartilagineum (Figure 8).
Now let’s revisit D. maxima. So we now have three different forms of this cross in our collection. How is this possible?
I was having a conversation about ‘genus jumping’ with a person in the United States about a month ago. Now this topic was new to me at the time but, in short, it is about crossing ferns from different genus that should not cross. And from all accounts, they can (they have the plants to prove it). The interesting bit lies in the technique they are using to do this and it would explain our three hybrids. The idea is that you sow one species first, and you sow it light (don’t use much spore). Two months later, you sow the second species heavy. Why do this you may ask? Well, as the prothalli matures, it produces the female organs. By waiting a couple of months, the first species has reached this point. Now we are surrounding these with the second species, which will be primarily male (to start with). This maximises the chance of cross fertilisation
between the two. And apparently, any hybrids will look most like the mother (the first species sown). If we apply this logic to our D. aspera hybrids, it means that one hybrid should look like the Doodia and the other like the Blechnum, which is true.
What about the third one though? So, this third one comes from North Queensland where the variant Blechnum cartilagineum var. tropicum lives. In my experience, this is generally a smaller plant that has shorter, wider fronds and is noticeably dimorphic. This could potentially explain the third hybrid (Figure 9).
And one final thing. On my block the B. cartilagineum drop spore a month or so before the D. aspera. With the logic above, that means that any hybrid here will most likely look like the Blechnum, which it does.
DWAYNE STOCKS
Dwayne has been involved with ferns for the past 15 years and runs a fern nursery with his wife Kylie. Both have a passion for all ferns and are avid fern collectors with one of the larger fern collections in Australia. Dwayne is also the developer behind the aboutferns website (www.aboutferns.org).
PETER D. HIND
Peter born in Derbyshire, England and emigrated to Australia in 1964. He worked for 40 years at the Royal Botanic Gardens & Herbarium in Sydney, where his interests in plants, particularly orchids, palms and increasingly ferns led to being joint curator of the ferns in the herbarium with Dr. Elizabeth Brown. He retired in 2008 and has maintained a keen interest in ferns, particularly in both growing and classification of Blechnum and
Doodia and the several natural and cultivated hybrids in this group. He leads walks in ferny areas, particularly in the Blue Mountains, west of Sydney, including the BPS trip in 2009, and many weekend excursions and study sessions with the Sydney chapter of The Australian Native Plant Society, Fern Study Group.
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