Lack of chlorophyll in plants is termed chlorosis. It can be total absence of chlorophyll, but is usually partial. A number of causes are commonly listed
  Deficiency of Fe or Mg in the soil
  Nitrogen deficiency
  Abnormal soil pH
  Waterlogged soil
  Compacted roots
  Exposure to some insecticides, sulphur dioxide or ozone
  Bacterial and other pathogens
I believe these can be ruled out. There are other plants of the same species nearby and other plants surrounding, all of which show no chlorosis. One would expect degrees of chlorosis in the vicinity with any of the listed causes. Some are unlikely such as exposure to chemicals, and water logging. Pathogens cannot be ruled out, but just one plant affected to this extent seems unlikely. This leaves a genetic cause or metabolic anomaly to explain this plant.

Chlorophyll-a, the form found in most vascular plants, consists of a porphyrin ring with a phytol tail. Haem, the active constituent part of haemoglobin also has a porphyrin ring, but chlorophyll has a central magnesium ion rather than iron. Chlorophyll is synthesized from succinyl-CoA and glycine. Neither of these is likely to be found deficient, but any one of the enzymes involved in the synthesis could be absent or non-functional. This points to a potential genetic defect. There are number of steps in the synthesis, each with a specific enzyme involved at each step, and thus a number of genes are involved. The final precursor to chlorophyll is protochlorophyllide, a highly photosensitive compound which creates free radicals. Thus there is strong regulation of free protochlorophyllide, with any not converted to chlorophyll being rapidly degraded. Over-regulation may therefore cause lack of chlorophyll, and again this will have a genetic basis.