Anastomosis as a term mostly known for it's use as a technique in surgical procedures, but the event or action the word represents has much wider applications. As a biological event it occurs unseen in the soils and moist places of the Earth trillions of times everyday.
Anastomosis is the joining of tubes Post-anastomosis, each tube becomes contiguous, contents such as matter, energy or information can be exchanged between them two-way
Mycology
IN hyphal systems anastomosis is the way bifurcating fungal hyphae form true reticulating networks. By sharing materials in the form of dissolved ions, hormones, and nucleotides, the fungus gains bidirectional communication with itself. The fungal network might begin from several origins, several spores, several points of penetration, each a spreading circumference of absorption and assimilation. Once encountering the tip of another expanding, exploring self, the finger tips press against each other in pheromonal recognition, then merge, creating a greater self, one organism, genetically one identity called a genet. This is one reason fungi are some the largest organisms we share this Earth with. Stretch for hectares though forests under the soil.
Self meets the other
Thread-like network organisms that fungi are, anastomosis is also sex. Two different haploid mating types - if compatible - merge. Forming another, morphologically similar mycelial wave front they/it continue to grow and explore. The main difference, each "cell" contain one of each nuclei. It/they are now a heterokaryon.
Imagine sexual fusion where not only do you enter/are entered, at one or two apertures but instead dissolve boundaries almost totally. Where everything except your nuclei are fused. Remaining genomically distinct but mutually building one physical manifestation in the somatic world. This is fungal reality.
Lineages and horizontal gene transfer - forks in the road rejoin
Imagine the branching trees of specieal divergence over time. Then imagine some of those tips somehow joining again to form networks in gene space. This is a metaphor for what happens during horizontal gene transfer - genetic information not only flows from ancestor to offspring, it also flows laterally between unrelated organisms. Imagine genetic information or endosymbionts exchanged between a pathogen, parasite or predator and its host or prey, the foreign entities integrated into their genomes or carried as co-reproducing passengers and passed onto their offspring. An anastomosis of lineages.
This anastomosis of lineages rarely occurs in eukaryotic organisms, but in the prokaryotic world the idea of organisms as identity, with distinct bounded lineages breaks down, bacterial are well known from their promiscuity with data.
When Molecular biologist study phylogenies of organism using marker molecules and create tree, depending on the molecule followed is not guaranteed to be the phylogeny of an organism. Just think, depending on your identity, your components, your organelles, some of your DNA can travel and have traveled different highways and byways than you.